I think I'm going to be using something like this for that old LCD feel.
wow that's amazing! awesome preview tool
Just hopped onto this to get an idea for the colors I want to use. Good share!!
Wow this is great, thanks for sharing.
Alpha is not allowed as it creates more colors unintentionally
To be a bit more specific, you essentially got one background color (the brightest one) and three darker tones to draw on top. You can't really draw with the background color.
For alpha transparency you can fake alpha by letting your sprites flicker (visible/invisible) between frames, which was rather common back then.
I think one could even add blending between frames to improve the effect, since the original Gameboy had quite some ghosting going on.
So in some way you can have alpha, but you'll have to fake it, if you want to stay authentic.
The point of the jam is not to completely and 100% authentically follow the GB limitations, it's a modern take on the GB while loosely following it's limitaitons.
I'd be tempted to port that to actual hardware. It'd require using a mix of sprites and BG tiles for the pieces, but it can definitely be done.
I've been thinking about doing that for a while actually, had the GB SDK sat on my desktop for ages but haven't gotten around to giving it a go yet.
Best part about this is if you add CGB support you don't have to bother with the second VRAM bank, you can just tweak the tints to your liking. However, you no longer have the BGP/OBP0/OBP1 registers so you'll have to do everything through the main CGB palette (in other words, fades will be different), and you'll use a different attribute bit to select the sprite palette.