There are other colours, but there should be consistency. Those stickers are samples for Kevin to choose from.
Red is subtle and difficult to see because often windscreens appear black. We've already made Red for 2011 Nationals.
Yellow really stands out.
White is boring.
Blue is subtle, just like red.
Aqua is somewhat different.
My other recommendation is "Copper" which is metallic brown, not shown in the photo.