If you sell a Game Boy color at Gamestop how much will you get?

There are lots of Nintendo gameboys:

GB,GB play it loud!, GBP,GBL(japan only), GBC, GBA, GBA SP, GBM

I'm guessing you're talking about an original 1989 GameBoy.

If you're talking about a 1989 GameBoy GameStop will not buy it because it is too old. GameStop will also not buy GB Play It Loud!,GBP, or GBC.

if you're talking about a GameBoy Advance, GameBoy SP, or GameBoy Micro

you will probably get about 10-15$ at GameStop.

My personal Opinion:

GameStop doesn't pay much for video game systems or Video Games unless they are recently released or best sellers. Selling it on eBay or in person will bring a better price, but you will not sell it very easily unless it's in good condition. You also probably will not get much if you sell your GameBoy games. In my opininon I wouldn't sell the GameBoy.