There's really no limit to the combinations of colors you can have. Try looking at sources from real life, or from other people's work.
it all depends if you want a coherent color scheme, or if you want each type of unit to have a different color... i for example paint my skinks green, saurus blue, monsters red - and all of them have white scales to give some coherensy. But i see many who choose a few colors to be the "theme" of the army. and if thats your preference i would recommend choosing what colors to paint in like this: 1. choose your main color scheme, and here i strongly reccomend choosing colors that are contrasts. black/yellow, purple/yellow/ red/white, blue/white/, green/orange, etc. this will make your models stand out, and will look great when finished. 2. Choose the slight differences there is gonna be between each type of unit, so there is some variation - and it doesnt just blend into one mash. if choosing a red/white color scheme, perhaps your saurus will be red with white scales, and your skinks will be white, with red scales - you get the idea. 3. Make sure that you paint all your models using the same technique. Dont drybrush highlight all your core units, and then use layering/blending on your monsters. If you do that, even though using the same colors, it will give your army a wierd look. But ofcause you can give your heroes, and other special things some extra time, but try not to make the difference too distinct, so it still looks like they belong. 4. Where is your army running around? choose a base theme aswell. and they in the mountains, jungle, plains, mud etc. Give all your bases the same look, this will also help to make your army look like an army. That was my 50 cent. /C1AA