What dkidd said. On larger projects, and especially for government (ie Port Authority of New York & New Jersey) jobs, it is frequently required by the specs and/or drawings. See here for an EMT product from Allied Tube, and here for rigid metallic conduit from Wheatland.
In most of my projects red conduit, JB's etc. is required to distinguish the fire alarm conduit from other systems. Fittings are not required to be red.
I was working in a hospital basement with a rather tall ceiling and watched a guy paint sprinkler pipe red. He had a 6" roller on a very long pole. Only the bottom half was painted. From the ground you couldn't tell it wasn't painted on top.