It's widely known that leaving a camera lens inside a car on a hot day is enough to melt lubricants inside and have them move where they shouldn't be. This used to be a common cause of "sticky aperture". Temperatures in a parked car on a hot day can reach 50-60 °C, so we can take that as a temperature at which damage is likely for this reason. Canon therefore have no real reason to make the rest of the lens handle any more than that.
Here's an experiment someone conducted to show the difference between a white lens and a black lens in the heat:
The test clearly shows the obvious. A white lens will stay cooler than a black one. It contains not even the claim that this has any impact on optical performance. No evidence here, either.
You're joking, right? I should put up with a less rigid element fixture that will eventually perish and require replacement, because some people want the lens to be black?
Again, there is NO EVIDENCE that making a lens white has ANY IMPACT at all on its optical performance. Nobody is suggesting anything be modified.
Larger sized L-lenses, such as the 70–200 mm and 100–400 mm zooms and longer focal length primes (300 mm+), usually have an off-white barrel (sometimes referred to as the color "putty") to reduce heat absorption under the sun that may otherwise affect the performance of the lens, as well as to identify Canon's lenses (for example at sporting events)
White DOES reduce heat absorption. No evidence of impact on optical performance here, either.
It's write on wikipedia here > http://en.wikipedia.org/wiki/Canon_L_lens
"It must be true! I read it on the internet." You have got to be kidding!
Lenses contain glass elements. These expand with heat. This is not usually a problem with compact lenses − the amount of expansion is small. But large lenses contain large elements and here expansion can bring a lens close to the limits of its design tolerances. A white surface reflects sunlight, helping to keep the lens cooler.
Again, no evidence that the heat absorb has ANY IMPACT AT ALL on optical performance.
And this one is write on Canon Website here > http://cpn.canon-europe.com …/black_or_white_lenses.do
Nothing like asking the fox about hen-house security! Canon has a vested interest here. NO VALID, UNBIASED evidence (or any other kind) here, either.
So the white color on large lenses it's to help against the heat !! ( Sony and Pentax do large lenses white also )
Nobody is even trying to make the point that white isn't a better color for dissipating/radiating heat. Similarly, NOBODY has provided any EVIDENCE that the heat difference affects optical performance.
Ed Rader sums it up nicely above. Its white because its white. Well said, and verifyably true. Refreshing.
If nobody has any scientifically verifyable, repeatable EVIDENCE that Canon's white lenses perform better in sunny/warm situations than Nikon black lenses, I suggest we let this topic go.