Quote Originally Posted by The_Vorpal_Tribble
Well, I believe you have to see a being to make a ranged touch attack anyways, so it should be a problem. Now, if the door was open the fog could enter within and that'd be a different thing all together.
To make a range touch attack you have to have a Line of effect, not a Line of sight. Diffrence being that Fog/darkness blocks line of sight, but not line of effect.

So a caster who has been blinded can still try to cast a ray spell, but he has a 50% miss chance.