diff --git a/index.html b/index.html
index 28c5ada2..8d40c2bb 100644
--- a/index.html
+++ b/index.html
@@ -153,6 +153,7 @@ body {
                <li><a class="dropdown-item" href="?platform=atari8-5200">Atari 5200</a></li>
                <li><a class="dropdown-item" href="?platform=atari7800">Atari 7800</a></li>
                <li><a class="dropdown-item" href="?platform=gb">Game Boy</a></li>
+               <li><a class="dropdown-item" href="?platform=gb.color">Game Boy Color</a></li>
                <li><a class="dropdown-item" href="?platform=pce">PC Engine</a></li>
                <!--
                <li><a class="dropdown-item" href="?platform=vectrex">Vectrex</a></li>
diff --git a/presets/gb/chase.c b/presets/gb/chase.c
index 735fb11d..7d8ec905 100644
--- a/presets/gb/chase.c
+++ b/presets/gb/chase.c
@@ -19,6 +19,7 @@
 #include "gb/types.h"
 #include "gb/hardware.h"
 #include "gb/gb.h"
+#include "gb/cgb.h"
 
 typedef uint8_t byte;
 typedef uint16_t word;
@@ -209,6 +210,15 @@ const Level levels[LEVELS_FIXED] = {
   { 16, 13, level_5 },
 };
 
+/*{pal:555,n:16}*/
+palette_color_t bkg_palettes[1][4] = {
+  { 0x2062, 0x318E, 0x6A28, 0x7714 },
+};
+/*{pal:555,n:16}*/
+palette_color_t fg_palettes[1][4] = {
+  { 0x73DB, 0x4BDC, 0x2B31, 0x14A3 },
+};
+
 /* Filled by generate_level() for endless mazes after the fixed set */
 char gen_row[MAP_H_MAX][MAP_W_MAX + 1];
 byte gen_w, gen_h;
@@ -784,6 +794,11 @@ void draw_cell(byte x, byte y) {
   }
 }
 
+void set_color_palettes(byte i) {
+  set_bkg_palette(0, 1, bkg_palettes[i]);
+  set_sprite_palette(0, 1, fg_palettes[i]);
+}
+
 void draw_hud(void) {
   byte lv = (byte)(game_level + 1);
   put_str_win(0, 0, "L");
@@ -1394,6 +1409,7 @@ void setup_graphics(void) {
   set_bkg_1bpp_data(0, 32, font_1bpp);
   set_bkg_data(BKG_BASE, 13, bkg_tiles);
   set_sprite_data(16, 12, sprite_tiles);
+  set_color_palettes(0);
   /* same font tiles for window HUD */
   for (x = 0; x < 20; x++) set_win_tile_xy(x, 0, 0);
   SPRITES_8x16;
diff --git a/presets/gb/gb/crt0.sgb b/presets/gb/gb/crt0.sgb
index b73d695d..55f18853 100644
--- a/presets/gb/gb/crt0.sgb
+++ b/presets/gb/gb/crt0.sgb
@@ -149,6 +149,9 @@ _refresh_OAM::
         .org    0x134
         .asciz  "Title"
 
+        .org    0x143
+        .byte   GB_CGB_FLAGS
+
         .org    0x144
         .byte   0,0,0
 
diff --git a/presets/gb/pakupaku.c b/presets/gb/pakupaku.c
index babccae6..8c1611da 100644
--- a/presets/gb/pakupaku.c
+++ b/presets/gb/pakupaku.c
@@ -15,6 +15,7 @@
 #include "gb/types.h"
 #include "gb/hardware.h"
 #include "gb/gb.h"
+#include "gb/cgb.h"
 
 typedef uint8_t byte;
 typedef uint16_t word;
@@ -81,6 +82,15 @@ byte sfx_timer;
 byte sfx_kind; /* 0=off 1/2=waka 3=eat 4=death 6=power */
 byte death_phase;
 
+/*{pal:555,n:4}*/
+palette_color_t bkg_palette[4] = {
+  0x2062, 0x5A31, 0x2A16, 0x6B11,
+};
+/*{pal:555,n:4}*/
+palette_color_t fg_palette[4] = {
+  0x1462, 0x463C, 0x2B31, 0x7FFF,
+};
+
 const uint8_t font_1bpp[] = {
   /* 0 space */ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
   /* 1 '0' */ 0x3C,0x66,0x6E,0x76,0x66,0x66,0x3C,0x00,
@@ -612,6 +622,8 @@ void setup_graphics(void) {
   set_bkg_1bpp_data(0, 35, font_1bpp);
   set_bkg_data(BKG_BASE, 4, bkg_tiles);
   set_sprite_data(SPR_BASE, SPR_TILE_COUNT, sprite_tiles);
+  set_bkg_palette(0, 1, bkg_palette);
+  set_sprite_palette(0, 1, fg_palette);
   SPRITES_8x16;
   BGP_REG = 0xE4;
   OBP0_REG = 0xE4;
diff --git a/presets/gb/siegegame.c b/presets/gb/siegegame.c
index db0abfa8..3692af0b 100644
--- a/presets/gb/siegegame.c
+++ b/presets/gb/siegegame.c
@@ -32,6 +32,7 @@ Controls: D-pad moves player 1, Start starts the game.
 #include "gb/types.h"
 #include "gb/hardware.h"
 #include "gb/gb.h"
+#include "gb/cgb.h"
 #include "gbtext.h"
 
 typedef uint8_t byte;
@@ -41,6 +42,11 @@ typedef uint16_t word;
 #define COLS 20
 #define ROWS 17
 
+/*{pal:555,n:4}*/
+palette_color_t bkg_palette[4] = {
+  0x6FFF, 0x5A31, 0x2A1F, 0x00,
+};
+
 ////////// GAME DATA
 
 typedef struct {
@@ -331,6 +337,8 @@ void play_game() {
 void main() {
   byte i, x, y;
   DISPLAY_OFF;
+  // set CGB background palette 0
+  set_bkg_palette(0, 1, bkg_palette);
   // unsigned tile indexing so ASCII codes work; must be set before
   // set_bkg_data(), which uses it to pick the VRAM tile base
   LCDC_REG |= LCDCF_BG8000;
diff --git a/src/machine/gb.ts b/src/machine/gb.ts
index 7ade561c..12c101da 100644
--- a/src/machine/gb.ts
+++ b/src/machine/gb.ts
@@ -17,6 +17,14 @@ function cgbColorToARGB(lo: number, hi: number): number {
   return 0xFF000000 | (b8 << 16) | (g8 << 8) | r8;
 }
 
+// CGB boot ROM default palette: 8 palettes of white/light-grey/dark-grey/black.
+// Each entry is a little-endian 15-bit BGR555 color (0x7FFF, 0x56B5, 0x294A, 0x0000).
+// Without this, CGB mode starts with palette RAM all-zeroed/white and DMG-style
+// games that rely on the default shades render blank.
+var CGB_DEFAULT_PALETTE = new Uint8Array([
+  0xFF, 0x7F, 0xB5, 0x56, 0x4A, 0x29, 0x00, 0x00,
+]);
+
 var GB_KEYCODE_MAP = makeKeycodeMap([
   // D-pad
   [Keys.RIGHT,   0, 0x01],
@@ -673,6 +681,7 @@ export class GameBoyMachine extends BasicScanlineMachine {
   sampleRate = 154 * 60 * 4; // ~36960 Hz: 4 audio samples per scanline
   overscan = false;
   defaultROMSize = 0x8000;      // 32KB minimum
+  aspectRatio = 10/9;
 
   cpu: SM83 = new SM83();
   ram = new Uint8Array(0x2000);       // Work RAM (C000-DFFF)
@@ -1576,8 +1585,10 @@ export class GameBoyMachine extends BasicScanlineMachine {
     this.vramBankSelect = 0;
     this.wramBanks.fill(0);
     this.wramBankSelect = 1;
-    this.bgCRAM.fill(0xFF);
-    this.objCRAM.fill(0xFF);
+    for (var pal = 0; pal < 8; pal++) {
+      this.bgCRAM.set(CGB_DEFAULT_PALETTE, pal * 8);
+      this.objCRAM.set(CGB_DEFAULT_PALETTE, pal * 8);
+    }
     this.bgCRAMIndex = 0;
     this.bgCRAMAutoInc = false;
     this.objCRAMIndex = 0;
diff --git a/src/platform/gb.ts b/src/platform/gb.ts
index 6d8efbfb..ab56b8e8 100644
--- a/src/platform/gb.ts
+++ b/src/platform/gb.ts
@@ -80,18 +80,15 @@ class GameBoyPlatform extends BaseMachinePlatform<GameBoyMachine> implements Pla
   }
 }
 
-const GBC_PRESETS: Preset[] = [
-  //{ id: 'hello_color.c', name: 'Hello Color World (C)' },
-];
-
 class GameBoyColorPlatform extends GameBoyPlatform {
 
   newMachine() {
     var m = new GameBoyMachine();
-    m.forceColor = true;
+    // not needed, gb.color sets the CGB header byte to 0x80
+    //m.forceColor = true;
     return m;
   }
-  getPresets()          { return GBC_PRESETS; }
+  getPresets()          { return GB_PRESETS; }
 
   getROMExtension() {
     return ".gbc";
diff --git a/src/tools/testlib.ts b/src/tools/testlib.ts
index 1699a709..e93dbda0 100644
--- a/src/tools/testlib.ts
+++ b/src/tools/testlib.ts
@@ -265,7 +265,7 @@ export function getToolForFilename(fn: string, platform: string): string {
   if (override) return override;
   // a specialization like verilog-vga has no params of its own; its root
   // platform's arch is the one that applies
-  var params = PLATFORM_PARAMS[base] || PLATFORM_PARAMS[getRootBasePlatform(platform)];
+  var params = PLATFORM_PARAMS[platform] || PLATFORM_PARAMS[base] || PLATFORM_PARAMS[getRootBasePlatform(platform)];
   var arch = params && params.arch;
   switch (arch) {
     case 'z80':
diff --git a/src/worker/builder.ts b/src/worker/builder.ts
index 59ca8b89..903c5ec2 100644
--- a/src/worker/builder.ts
+++ b/src/worker/builder.ts
@@ -135,17 +135,16 @@ export class Builder {
    * one source file's directives can't follow the next build around.
    */
   paramsForBuild(platform: string) {
-    const base = getBasePlatform(platform);
-    if (!this.buildParams[base]) {
-      const params = PLATFORM_PARAMS[base];
+    if (!this.buildParams[platform]) {
+      const params = PLATFORM_PARAMS[platform] || PLATFORM_PARAMS[getBasePlatform(platform)];
       const copy = {};
       // values are strings, numbers, and arrays of those
       for (const key in params) {
         copy[key] = Array.isArray(params[key]) ? params[key].slice() : params[key];
       }
-      this.buildParams[base] = copy;
+      this.buildParams[platform] = copy;
     }
-    return this.buildParams[base];
+    return this.buildParams[platform];
   }
 
   async executeBuildSteps(): Promise<WorkerResult> {
diff --git a/src/worker/platforms.ts b/src/worker/platforms.ts
index a337ec49..2bd40a2d 100644
--- a/src/worker/platforms.ts
+++ b/src/worker/platforms.ts
@@ -395,6 +395,7 @@ export var PLATFORM_PARAMS = {
         '-g', '_shadow_OAM=0xC000',
         '-g', '.STACK=0xE000',
         '-g', '.refresh_OAM=0xFF80',
+        '-g', 'GB_CGB_FLAGS=0x0',
       ],
       wiz_sys_type: 'gb',
       wiz_inc_dir: 'gb',
@@ -410,8 +411,15 @@ export var PLATFORM_PARAMS = {
     },
 };
   
-  // SMS/GG mode-4 variants of the shared libcv common.[ch] (2 bytes per tile, 32x28)
-  PLATFORM_PARAMS['sms-sms-libcv'] = { ...PLATFORM_PARAMS['sms-sg1000-libcv'],
-    extra_preproc_args: ['-I', '.', '-D', 'CV_SMS', '-D', 'CV_MODE4'] };
-  PLATFORM_PARAMS['sms-gg-libcv'] = PLATFORM_PARAMS['sms-sms-libcv'];
-  
\ No newline at end of file
+// SMS/GG mode-4 variants of the shared libcv common.[ch] (2 bytes per tile, 32x28)
+PLATFORM_PARAMS['sms-sms-libcv'] = {
+  ...PLATFORM_PARAMS['sms-sg1000-libcv'],
+  extra_preproc_args: ['-I', '.', '-D', 'CV_SMS', '-D', 'CV_MODE4']
+};
+
+PLATFORM_PARAMS['sms-gg-libcv'] = PLATFORM_PARAMS['sms-sms-libcv'];
+
+PLATFORM_PARAMS['gb.color'] = {
+  ...PLATFORM_PARAMS['gb'],
+  extra_link_args: PLATFORM_PARAMS['gb'].extra_link_args.map(arg => arg === 'GB_CGB_FLAGS=0x0' ? 'GB_CGB_FLAGS=0x80' : arg)
+}
diff --git a/src/worker/tools/mcpp.ts b/src/worker/tools/mcpp.ts
index 978cda3f..9d613e1f 100644
--- a/src/worker/tools/mcpp.ts
+++ b/src/worker/tools/mcpp.ts
@@ -11,7 +11,7 @@ function makeCPPSafe(s: string): string {
 export function preprocessMCPP(step: BuildStep, filesys: string) {
     load("mcpp");
     var platform = step.platform;
-    var params = PLATFORM_PARAMS[getBasePlatform(platform)];
+    var params = PLATFORM_PARAMS[platform] || PLATFORM_PARAMS[getBasePlatform(platform)];
     if (!params) throw Error("Platform not supported: " + platform);
     // <stdin>:2: error: Can't open include file "foo.h"
     var errors = [];
diff --git a/src/worker/workertools.ts b/src/worker/workertools.ts
index 766b70e5..17ee283c 100644
--- a/src/worker/workertools.ts
+++ b/src/worker/workertools.ts
@@ -19,7 +19,6 @@ import * as oscar64 from './tools/oscar64'
 import * as xa from './tools/xa'
 import * as dialog from './tools/dialog'
 
-import { PLATFORM_PARAMS } from "./platforms";
 
 export const TOOLS = {
   'dasm': dasm.assembleDASM,