ok lah.
on a serious note, canon's white telephoto lenses are painted white on the external barrel. whether for technical reasons (flourite having heat issues?) or for marketign reasons (white is more attention grabbing then black?), we never will really know. all we know is that they are very high quality lenses, and are designated with the red ring in front of the barrel the "L" for "luxury" insignia) (except for the DO lens => green ring)
the thing is that white lenses is a phrase that 99% of the time refers to canon's telephoto lenses for 35mm SLRs