And if Wikipedia is to be believed it's presented in a eye wateringly high resolution of 112p.
This high of res.
Edit: Of course the bit rate was pretty damn low as well. Here's a comparison video I found. This comparison uses the higher bit rate version from the Shrek GBA video cart not the Shrek+Shark Tale video cart though so keep in mind, this is the better version.
How many colors does the Gameboy advance support? It can't be more than 256.
32768