It varies from project to project. In some stories, having it black and white can set a great atmosphere (for example, "detective noir" stories). Adding colors can take away from the atmosphere sometimes unless it's very muted. Others, you just WANT to see them in color, such as fairy tale-like stories. Overall, though, I don't mind either way. ^_^
I like both color and black and white comics. Each approach has their own challenges. The success of either is dependent on the story and the skill of the artist. I agree that for me there are some comics that I cannot image being anything other than black and white because to do them in color would mask the dynamic use of contrast.
I like both, as long as they're done well. I've seen some really awful black & white and some equally awful color. I've also seen some awesome examples of both. It really depends on how it's executed and what the subject matter is.
Well, I've always been partial to colored comics, as long as they're well-done. Sometimes there is too much color that does not mesh...in which case B&W would look cleaner and easer to read.
In terms of TV/movies, it depends on the genre. Many Hitchcock film noire style movies would not have the same creepy, darmatic sading in color.
I have to admit there are some fantastic B&W movies, but I do prefer color.
As far as Comics go, the fact that it is/isnt in color is the last thing I consider, and by the time I even think about it, I already know if I like the comic.
Keep on Stripping! (Updating! you pack of dirty dirties!)
I have never seen a comic transition to color, and thought "I wish it was still B&W".
The main reason I prefer color is that it makes the art easier to "read". I don't have to try to ID characters by nostril width, or hope names are dropped in the dialog. I can just remember "person with red hair", "person with green skin", etc. It also distinguishes things from the background - SMBC generally has extremely dull, desaturated, dark backgrounds, while the characters wear much brighter, contrasting colors. So I can *immediately* tell what those characters are doing.
Taking a look through my "updates 3-4 times per week" folder, I see 6 out of 20 that are primarily black and white. All six of those are notable for clean, high-contrast art - XKCD is the extreme case, where the art is *extremely* "simple-looking". You can tell what the background is because it's white, while everything black is either a panel border, a character, or an important item. Or a graph joke, because who doesn't like graph jokes? The rest are still very clean, high-contrast B&Ws - Starslip, Basic Instructions, etc.
I've personally seen several comics transition from B&W to color while reading them. Dr McNinja stands out as the best example. The original art was fine. A bit rough, but fine. Then it went color, and never looked back. And it allowed for *new* things to happen - I cannot imagine King Radical in monochrome, since his design's so complex. And the time portals - in B&W, you'd have just a swirly thing. In color, you've got an otherworldly, contrasting purple.
On one last note, I've quit reading various comics for various reasons. The only ones I've quit because the art sucked, were B&W. Just saying.