There are tons of fun colour activities....
http://www.pinterest.com/pin/7810999327984030/
http://www.pinterest.com/pin/7810999326874974/ This one you could do over a few days and use different hand colours to mix. ie Red and BLue, Blue and Yellow, etc to show the end result
http://www.pinterest.com/pin/7810999326177184/
It's a great idea to make some of these activities/tools for your daycare and you will have them year after year to teach the children when they get to that stage
Another one I like I having an egg carton and painting each spot in an egg carton a colour and then sorting the correct coloured pom pom into each spot in the egg carton
http://www.allkidsnetwork.com/crafts...loud-craft.asp is alsoa simple craft but lets you talk about the colours.
Good books for colours are "Freight Train" and "Brown Bear, Brown Bear What Do you See?" and make the kids tell you the colour of each train or each animal on the page. It's good practice