I once came across a page that had multiple photo's of a tank under different K lights and let you select 2 and compare them. Stupidly I didn't bookmark this but if you find it please let us all know... I'm pretty sure it was done by Sanjay Joshi but can't find it on his site and no amount of googling has helped me.
This is quite a cool bulb comparison excercise that shows what the difference looks like in out tank. Although they comparing 250W MH bulbs it will give you an idea of what the different kelvin ratings look like.
Takes a few minutes to load but worth it