diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index d1121673d..3b9d231f9 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -315,6 +315,8 @@ enum DivDispatchCmds {
 
   DIV_CMD_WS_GLOBAL_SPEAKER_VOLUME, // (multiplier)
 
+  DIV_CMD_FM_ALG,
+
   DIV_CMD_MAX
 };
 
diff --git a/src/engine/platform/genesis.cpp b/src/engine/platform/genesis.cpp
index be99595cb..2ef13b1aa 100644
--- a/src/engine/platform/genesis.cpp
+++ b/src/engine/platform/genesis.cpp
@@ -1539,6 +1539,9 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
       break;
     case DIV_CMD_PRE_NOTE:
       break;
+    case DIV_CMD_FM_ALG:
+      if (c.value>7) break;
+      rWrite(ADDR_FB_ALG+chanOffs[c.chan], c.value&7);
     default:
       //printf("WARNING: unimplemented command %d\n",c.cmd);
       break;
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index 2085f279f..e5c0050d6 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -309,7 +309,9 @@ const char* cmdName[]={
   "SID3_CUTOFF_SCALING",
   "SID3_RESONANCE_SCALING",
 
-  "WS_GLOBAL_SPEAKER_VOLUME"
+  "WS_GLOBAL_SPEAKER_VOLUME",
+
+  "FM_ALGORITHM"
 };
 
 static_assert((sizeof(cmdName)/sizeof(void*))==DIV_CMD_MAX,"update cmdName!");
diff --git a/src/engine/sysDef.cpp b/src/engine/sysDef.cpp
index d9bf59f94..c235ac443 100644
--- a/src/engine/sysDef.cpp
+++ b/src/engine/sysDef.cpp
@@ -502,6 +502,7 @@ void DivEngine::registerSystems() {
     {0x5e, {DIV_CMD_FM_D2R, _("5Exx: Set decay 2 of operator 3 (0 to 1F)"), constVal<2>, effectValAnd<31>}},
     {0x5f, {DIV_CMD_FM_D2R, _("5Fxx: Set decay 2 of operator 4 (0 to 1F)"), constVal<3>, effectValAnd<31>}},
     {0x60, {DIV_CMD_FM_OPMASK, _("60xx: Set operator mask (bits 0-3)")}},
+    {0xb3, {DIV_CMD_FM_ALG, _("B3xx: Set algorithm (0 to 7)")}},
   };
 
   EffectHandlerMap fmOPMPostEffectHandlerMap(fmOPNPostEffectHandlerMap);
diff --git a/src/gui/guiConst.cpp b/src/gui/guiConst.cpp
index 561bb632f..40938b42d 100644
--- a/src/gui/guiConst.cpp
+++ b/src/gui/guiConst.cpp
@@ -478,7 +478,7 @@ const FurnaceGUIColors fxColors[256]={
   GUI_COLOR_PATTERN_EFFECT_SYS_PRIMARY,
   GUI_COLOR_PATTERN_EFFECT_SYS_PRIMARY,
   GUI_COLOR_PATTERN_EFFECT_SYS_PRIMARY,
-  GUI_COLOR_PATTERN_EFFECT_INVALID,
+  GUI_COLOR_PATTERN_EFFECT_SYS_PRIMARY,
   GUI_COLOR_PATTERN_EFFECT_INVALID,
   GUI_COLOR_PATTERN_EFFECT_INVALID,
   GUI_COLOR_PATTERN_EFFECT_INVALID,