Throwing my two cents in:
To get the Game Boy Pocket color just comment out the GB.params as recommended by Duimon and using a Core that can set Game Boy Palette to Game Boy Pocket, ie mGBA.
I have created a topic specifically for changing colors of Duimon’s work. The settings can put in a slangp file and put in Duimon’s override folder.
#reference "../../Duimon-Mega-Bezel/Presets/Standard/Nintendo_Game_Boy_Color/GBC-[STD]-[LCD-GRID].slangp"
HSM_NON_INTEGER_SCALE = "48.370000"
HSM_DEVICE_HUE = "249.000000"
HSM_DEVICE_SATURATION = "100.000000"
HSM_DEVICE_BRIGHTNESS = "100.000000"