If you just want to play baseball casually with friends, it is unlikely that you will have the baseball uniforms that many baseball players wear when they play. Even without these uniforms you can identify one team from the other just by telling people to wear different colors of shirt. Even better, you can find great shirts that even are made for baseball wear.
There are many different types of baseball shirts that are designed in a very specific and comfortable style that is perfect for when you are playing baseball. I personally enjoy wearing a special Henley shirt when I play baseball since I find these comfortable and stylish. I am hopeful that I will be able to buy some more of these shirts for when I play baseball with friends this summer.