All school buses in the US are yellow, as far as I know. It's probably a safety thing so that drivers can easily identify a school bus and stop when its loading or unloading kids. It's a law that drivers cannot pass a school bus (in either direction) if the red lights are flashing, which indicate loading/unloading. Most have a stop sign that swings out from the side when the red lights are on.

Do you have a similar law?

Hmmm. Now that you mention it, most of our school buses are that long nose style, but I have no idea why. I have occasionally seen the cab over style, but they are rare. Some communities also use smaller "stubby" looking buses that carry fewer students and even cars with a "school bus" sign on the roof.

You got me curious about this, so I googled it. This Wikipedia entry more or less answers your question. It seems to be wrapped up in the need for standardization both to meet U.S. federal regulations and to profitably market a consistent product.

http://en.wikipedia.org/wiki/School_bus

Thanks for bringing this up. As my 10th grade biology teacher used to say: you learn something new every day.