I would think that colouring on damp fabric would allow the colour to spread as the quilt dried.
As to fixing it, I might get a toothbrush and screen, mix up a variety of the same colours of the pencils in acrylic paint....I would then dip the toothbrush in paint and rub the brush over the screen at about 8 inches? And add dots of rainbow colours over the whole surface of the quilt. We used to use this method in school to add a spray of colours on a surface. Some rubbed a toothbrush over a comb to spray the paint for larger spots. You could also use a mist bottle of paint to add colours. Good Luck and with whatever you decide to do, try it on a sample first.