Paint absolutely warms up a space like nothing else. For a 12 x 12 room, one gallon is enough. Most say you should do two coats but I can usually get away with one. And it is CHEAP! Behr paints from Home Depot are great and a fantastic deal -- only $20 for a gallon.
My favorite example of how paint transforms a room is my stepdaughter's room. We used blue for the walls and she picked out three more colors to add...this is what we came up with:
I did this for $50 -- $20 for a gallon of paint and $10 each for three quarts. Am I wrong? Total transformation! If you would like more info on how do the grid, just let me know. It looks much harder than it is. (I say that a lot, huh?)