There are many ways out there to make sure the colors of your fabric don't bleed into other fabrics in your quilts. I am sure there are many ways to make sure the color of your fabrics stay as bright or close to it after washing. I don't know them. Today I am going to tell you about my way of setting colors in fabrics, that not only works in fabrics for quilting but in clothing as well. I use this method with all my bright and dark colors. This way has never failed me and I have been doing it for almost 12 years now.
2 cups white distilled vinegar (I use Flavorite, it doesn't have to be the expensive stuff to work)
enough cold water to cover your fabric, water should be close to ice cold.
Submerge your fabric into the cold water and make sure it is completely wet. Let sit in the sink for 2-6 hours, but no more then 24 hours. Take out of the cold water and squeeze, don't twist just squeeze, out excess water and machine wash like normal.
This method works for up to 4 or 5 yards of fabric, for more then 5 yards add more vinegar about 1 cup per 2 yards and of course add more cold water to cover the fabric.
For jeans, add 3 cups of vinegar to the cold water and let sit for 6-8 hours. Keeps your black jeans black! Turn jeans inside out before placing in the washing machine.
I hope this helps you keep your colors looking the way you want them too.