I found this picture whilst looking for images to make signs with:
It made me wonder if in fact the suits are made in certain colours to reflect the type of hazard they are designed for.
Short answer is no. I thought it would have been cool if they were colour coded, but from what I have seen on the internet (and as I always say - it must be true because it is on the net) the most common colour is yellow, followed by green.
One good point from all this is that you only need to paint up one set of Hazmat figures for your zombie game.