According to the description it seems you鈥檙e allowed to use anything you want as long as it lets you adhere to the restrictions, that is 84x48px, the 2 specified colours, no more than 12 keys and monophonic audio. If GBStudio lets you do all that then it should be good 馃槈馃憣
I think you can use it but you'll need to limit the screen area of everything that the player can see to only 84x48 pixels which is less than a quarter of the GB screen size of 160x144. (If you doubled that, you'll get 168x96 which has higher width than GB size and that will probably disqualify you.) If you can manage to make it work, I would like to see that!
You can change the color Palette in GBStudio, GB uses 4 colors but they can be changed, especially if you run the game as GBC or Web. (GB Studio can export to web too.)
