lighter color roofs do last longer and they keep the attic cooler in
the
summer. However, studies at the University of Florida have shown that
if you have adequate attic insulation (R-30+) then the attic
temperature
has no discernable impact on the house's heat load.

Thats very likely BUT lighter colored roofs reflect more heat thus the
attics are cooler so the shingles last longer. I recently sold a home
with gable end and ridge vent. The home inspector wrote it up because
the attic was 20 degress warmer than the outside on a hot july day. He
recommended adding power vents to the roof.

Light colored roofs just make everything easier

you want a cool attic if your like many and use it for storage.