This is going to pickle my brain then. A friend used to have a Master System 2 (I think it was) and it had some odd adapter that you could plug into the cart port. He said it was used to play Game Gear games *shrug*. Looked like a Spectrum memory expansion pack.
The GG has an extended palette, if you want to play a GG game on SMS you have to hack the game to use valid SMS palette entries. Also the GG has an additional button not on the SMS controller, the Start button. Which means another thing you have to hack.
The GG doesn't use the whole screen, it still has 256x192 pixels (like SMS) in memory but it only displays 160x144 of those on screen. Outside those pixels you may have pretty much anything. Could be perfectly useful level graphics, but it may just as well be garbage.
- Ok, you must admit that was the most creative cussing this site have ever seen -
Well said. Often, GG games that were converted from SMS games can, in many emulators, have the border removed, to find that the game is nearly identical to the SMS game, as everything beyond the border is still visible.
You'll find that most of the games that appeared on both systems don't make much use of the Game gears extended palette. Only exclusive Game gear games like Ristar or Sonic Triple trouble have a noticeably higher colour count.