Denons dark? No way! Dark sounding has no correlation to open/closed form factor of the headphone itself.
Dark, veiled, laid back sounding are all the same thing just different terminology use, the LCD2's are laid back/dark sounding and definitely not forward/bright sounding like your Grado or HD800.
The HD650 is warmer sounding than the LCD2 rev.2's. HD600 is neutral with a slight emphasis on the upper mids, much more neutral than both the 650 and LCD2's to these ears. But the LCD2's do hit the low octaves very nicely.