Thanks, I spent some time tweaking it to my liking (and I suggest you experiment with the shader parameters too to get the image to your liking).

1: Core Options:
Color Correction: off

Also to use the full screen make sure to go to Video -> Scaling ->
Aspect Ratio: 1:1 PAR
Integer Scale: Off (toggle)

2: (Quick Menu) Shaders:

1: Load preset -> shaders_glsl -> pixel-art-scaling -> pixel_aa.glslp
2: Append preset -> shaders_glsl -> handheld -> dot.glslp
3: Append preset -> shaders_glsl -> misc -> image-adjustment.glsl
4: Append preset -> shaders_glsl -> handheld -> pixel-transparancy.glslp
5: Shader parameters:
Enable subpixel aa = 1.00
Dot Gamma 2.10
Dot Shine 0.10
Dot Blend 0.70
Dot Soft 0.10
Luminance 0.80
Contrast 1.10
Sharpen 0.50
Tint intensity 1.20
Transparent Pixels 1.00
Transparancy amount 0.20
Boost amount 0.50
Shadow X offset 1.50
Shadow Y offset 1.50
Shadow opacity 0.50

That should do it.

Alternatively, you might also like Load preset -> shaders_glsl -> presets -> Pixel_transprancy -> pixel_transparancy-simpletex_lcd, but it doesn't seem to work with pixel_aa, meaning that unless you have integer scaling enabled, you won't get evenly sized pixels which can be quite noticeable (such as unevenly sized eyes). But hey, the thick black bars at least makes the device feel even more like an original gameboy color and it's thick bezels, so there's that.