One thing you never had to worry much about in B&W film days was the blue color cast outdoors on a bright, blue sky day. With color, it's different. The blue sky tends to turn everything, white objects especially, slightly blue. But when you're out there on the street your eye compensates and tells you white is white. Unfortunately, the camera doesn't compensate. In film transparency days you bought "daylight" film that responded more or less correctly to a light source at about 5500 degrees Kelvin. With digital, if you shoot .jpeg and set your camera on one of the outdoor daylight settings, you get something similar to the results you'd get with daylight color film, but almost everyone nowadays shoots raw with in-camera color balance set on automatic. I know I do. If you do that, some of your shots will be fine, but some will have an obvious blue cast. You need to check every shot to make sure the blue cast isn't visible, and adjust if it is -- either with Photoshop's "White Balance" menu, or, better yet, by picking up the White Balance dropper and clicking on something you know is white or middle gray.
I see the problem in an awful lot of pictures put on LuLa for critique, and in an awful lot of tourist pictures, but I've tried to be polite and not mention it. I think I'll stop being that polite if the photographer is asking for criticism. I wonder if anyone else has noticed the problem.
