I don't know much about this stuff but i would say it is an 50% chance too.

In your ball example:
I wouldn't consider RB and BR as a different possibility.
If you say one ball is red, the other one can be either Red or Blue, which is 50/50. You can't consider the BR case anymore as you know the first one is R so it will be Rx where x is wether B or R.

Many years ago my teacher gave me this probability theory:
You have 3 cups infront of you and in one of those cupse is a marble. Now you pick a cup, and you have a 1:3 chance to get the right cup.
After you chose a cup, the gamemaster is so kind to show you one of the cups that doesn't have the marble and takes it out of the game and asks you if you wanna stick with your cup or choose the other one.

So now it's always smarter to switch to the other cup cause suddenly your winning chances are 1:2. We tried this in many games and your winning chance IS higher when you switch in the second turn.

Maybe some of you (german speaking people) remembers "geh aufs ganze" and there you often has 3 envelopes and two had the Zonk (the bad price). They always let you choose one and sometimes say "ok i give you a hint, this one is a zonk and i'll take it out".

So like inthis example, if you take out one envelope, you take out a possiblity so your chances increase to 1:2.
I think it's the same with the balls. If you say the one is R, then you actually can't consider the case BR and BB.