no its not 50%

There are 4 outcomes when drawing balls:

(chance - color color)
1/4 - R B
1/4 - B R
1/4 - B B
1/4 - R R

So when saying that at least one is red,
then you sort out the
B B possibility, leaving you with

1/3 R B
1/3 B R
1/3 R R

so now:

1/3 R B (one is Red, the OTHER Black)
1/3 B R (one is Red, the OTHER Black)
1/3 R R (one is Red, the OTHER Red)

gining you a chance to have only 1/3 that
the OTHER is Red