Is there any way to know what is asked when you practice, i.e. traditional or simplified? Since I practice both I often begin with one when I should write the other one.

A lot of people are asking exactly this since the new system went up, which firmly lets us know we've made a bad design choice and need to fix it. See this thread:
http://www.skritter.com/forum/topic?id=1101552

It's the color of the box behind the characters in the prompt: goldenrod for simplified, pink-red for traditional, blue for unambiguous.

On our list of things to do is add a touch of interactive help, so for example a little popup could appear explaining this system the first time you went to practice with both forms of characters enabled.

sorry, didn't see that. thanks.
and just as whiteto2 said, it's easy to use once you know.

...by the way, what colors can't a color blind person see, is it red and green. anyhow, then a another kind of indication might be a future implementation if there's a need.

I haven't heard of anyone having problems differentiating these colors. As far as I know, it's usually red and green, sometimes blue and green, or green and yellow. Depends on the person and the hues.

We'll keep trying to make stuff that doesn't rely solely on red vs. green, and hope users let us know if there are further problems.

Just FYI, I'm mildly red/green color blind. I have no problem at all differentiating the colors.