graphics issue - some things very dark

I have an issue where many things, such as hair, jewellery, even sand at a beach, and the sea all appear very, very dark while other things - such as clothes, skin, eyes etc all appear as normal. This is relatively recent - over the past few weeks, but happens for me and my alt on my imac, but not, so far on my macbook. It happens in the standard viewer and in snowglobe.
I've played with all graphics settings, with no effect. I've emptied the cache. I've rebaked and relogged. no effect.
With the hair, I can return it to normal colour by going to edit - texture - and turning off 'full bright'. I immediately get the proper color for the hair. But I can't do this with the sand or the sea....
Anyone else encountered this? Or have any suggestions?
I think it must be something to do with my graphics card and a change in how SL is handling light, because I never used to have these problems, and nothing has changed on my machine (apart from regular OS updates - I'm on Snow Leopard 10.6.2)

OK, solved. If you have this issue, in the main viewer, go to preferences, graphics, hardware and turn off atmospheric shaders.
Not sure that you can do this in Snowglobe though. (Snowglobe is an alternative viewer, btw)

Thanks for that info, Ive had that happen to me in windows every so often and found it rather bizzare.

Just a little word of caution to the proposed solution. The issue is real, and the culpit is the difference of the shaders. But, if you turn off the atmospheric shaders, you do so on your screen, but not on mine. So, if you adjust your new prim feet on your screen to look good without the atmospheric shaders turned on, then - how do you think you look on my screed - right, you have dirty (dark) feet.

Unfortunately there is nothing that can be done here it seems, and at least it is nice to look good on your own screen.