You could have a single big square sticker type sign that's white, as a background, and then have your proper company colours on it. You might find it's cheaper too as it may be just one sheet and not lots of letters the guy has to peel off and stick on one by one so the labour should be less.
You could also consider something like this Boss Dog | Van Graphics - Van signage, advertising which they use a hot air gun to stretch over the van. See the "express business services" van, that's a light grey van with a dark grey vinyl thing on it. And on the vinyl thing, which could then be any colour, you could have your company logo/colours. And look at the "sure flow" van here too: Boss Dog | Gallery - van sign writing, car sign writing, bike stickers and graphics