Voted dark since I like the Sennheiser house sound a lot. I agree a slightly darker sound might make lots of recordings and equipment more tolerable. Also, at least for me, a slightly darker balance is way less prone to fatigue than a slightly brighter presentation. This might be very ear/person dependant though. After a recent hearing test I was told I'm more sensitve to higher than lower freqs in the range below 8K, though I think that test wasn't very conclusive/accurate.
My top choice of headphone is HD650+Zu, some regard the combo as dark, some as too bright (?), obviously YMMV. I think it just sounds great, especially powered by a Dynahi.
Despite this general preference for slightly-darker sound, I must say I do like the Grado SR-60 sound a lot, as well as HP-2's (properly amped, e.g. Microzotl), AKG-501, and needless to say, the Orpheus, neither of which are regarded as dark headphones.