No Sweat... If you do choose to go with tempera paints and you have acsess to Hobby Lobby, their tempera paints (pre-mixed) are the best deal, and usually are on sale for 30% off, or you can use the 40% coupons..
All you need is Red, Yellow, Blue, White, and Black. You can mix any other color you want with those.. But I also grabbed bottles of brown and green anyway..
Keep in mind though, that tempera paints are water-soluable, even after they dry...