Summer List: Tie Dyein' Awayhayyy

Another check off the summer list: Tye Dyed shirts.
This was super fun and our 4 boxes of Rit Dye managed to color 4 adult shirts, 4 adult tank-tops, 4 kids shirts, and 5 baby onsies (this is a gift, shhh). We had a really good time and they came out awesome.
Awesome that is, until we washed them, which the box said to do. All the bright vibrant colors ran together until the colors were subtle and the white was all muted green. Still good... but not nearly as bright.
What did I do wrong? How do I keep the nice, bright, vibrant colors?