If your talking about the unusual colors it's because you are running the game in 16-bit color mode.
Go to options > display settings and advanced, there you should see your screen resolution and next to it the color type. I suggest you change it to 32-bit if it's not set to that already, also change the screen size to your native resolution (I'm sure your GFX card can handle high resolutions in GTA:SA)
Hope this helps..