Sandra,
You are going to find so many different opinions on this subject!
Even the quilting Diva's with tv shows have different opinions.
I do not prewash unless it is a dark fabric. As Alex said on her show, fabrics are so much more colorfast than they were years ago.
I have never had a quilt 'bleed' when washing it, but, I do use the color catcher sheets just in case. I did have a dark blue fabric that after 4 washes in vinegar then soaking in salt would not stop bleeding so I was afraid to use it.
You can soak a corner of the fabric in a small amount of water and check it the next morning or lay it wet on a white cloth.