The difference is in the quality of the steel and heat treatment of same. I'm surprised that the black is Professional S.
I have an extra Henckels Chef's Knife given to me by an in-law, and its black on the blade, if there is anything on the blade at all (it looks just like, but is not a Pro S). However, it won't cut butter and you can't sharpen it - it's made from a cheaper grade of steel.
We do have an entire set of Pro S & I'll look at it tonight when I get home. My Pro S chef's knifes, at the least, have the red symbols stamped on the blades. If its only a picture on a website, perhaps they made a mistake.