Add GB Color Correction core option

src/libretro/libretro.cpp

@@ -187,6 +187,11 @@ static void set_gbPalette(void)
         gbPalette[i] = pal[i];
 }
 
+static void set_gbColorCorrection(int value)
+{
+    gbColorOption = value;
+}
+
 extern int gbRomType; // gets type from header 0x147
 extern int gbBattery; // enabled when gbRamSize != 0
 
@@ -1194,6 +1199,15 @@ static void update_variables(bool startup)
         if (lastpal != current_gbPalette)
             set_gbPalette();
     }
+
+    var.key = "vbam_gbcoloroption";
+    var.value = NULL;
+
+    if (environ_cb(RETRO_ENVIRONMENT_GET_VARIABLE, &var) && var.value)
+    {
+        int val = (!strcmp(var.value, "enabled")) ? 1 : 0;
+        set_gbColorCorrection(val);
+    }
 }
 
 // System analog stick range is -0x7fff to 0x7fff

src/libretro/libretro_core_options.h

@@ -145,6 +145,17 @@ struct retro_core_option_definition option_defs_us[] = {
         },
         "disabled"
     },
+    {
+        "vbam_gbcoloroption",
+        "(GB) Color Correction",
+        "Applies color correction which fixes colors in some games games.",
+        {
+            { "disabled",  NULL },
+            { "enabled",   NULL },
+            { NULL, NULL },
+        },
+        "disabled"
+    },
     {
         "vbam_turboenable",
         "Enable Turbo Buttons",