Welcome to the world of washers!
I haven't figured out a way of telling which fabric might have excss dye by "just looking at it" yet.
I think it's just as much of a bother to cut off a little piece to see what it will do as it is to dunk the whole piece. The added benefit - no little corner is missing from the piece.
Of the hundreds of fabrics I've washed, I think I've come across less than 10 that I consider real stinkers.
An orange - that one was the worst
A teal
A green
A purple
A navy
A yellow
A stinker is one that continues to color the water a lot after ten dunkings.
Don't recall any red being a real bleeder after I got the initial excess dye out of it.
My comfort level is: Can I put this in the wash with a very light color and not worry about the light color being a different color when the load is done.