Well, two answers weren't really helpful were they? And the second guy ain't got a clue!
In fastpitch (except for 10U girls) the ball is 12" in diameter. In slowpitch the ball is 12" in diameter. 12" and 12" are both the same size!!
There is no difference between a fastpitch glove and a slowpitch glove. There IS a difference in a baseball glove, it has a smaller pocket. There are some size requirements in FED ball, but most gloves you will consider are legal.
You can not have a glove which is more than 2 colors, (this excludes lacing and printing). A totally white, gray, or optic colored glove is illegal.
A red, white and blue glove then would be illegal, but a red and white glove with blue lacing would be legal! Crazy rules!
Find one that fits well and feels good. Treat it as a friend!