You can also try painting them as your eye sees it,for each block vary your color shades,one block mix a metalic red,blue,purple,next block try adding or subtracting a color,and so on.I also have tried a piece of chrome wraping like you would get from a candy bar. Paint it clear red as gino said then thin your met paints way down,then take a little dollip from each color and put it on the clear red, then mix each color together,you don't want to mix each one perfect just so each color kind of blends together.If you look at it from a distance and from different angles you will see that changes it colors.When it dries cover with a high gloss varish.