Hi, I am primarily a handquiltier and I love colored thread. I just finished quilting a raffleqult for our local Linus Chapter. It has pieced blue stars some large open spaces that are yellow and a floral print border. I handquilted the whole thing in blue thread. While it is not so visible on the blue areas it certainly pops on the yellow sections. At our local Senior Center I help quilt their raffle quilts. Last year we did a Stack and Whack star pattern that was made of primary colored stars on a black background. I talked them into using varigated thread. It was really pretty and the person who won the raffle was delighted. I also prefer colored thread as it shows up the quilting on the back of the quilt which is usually a solid color or at least the same fabric all over.
I make lots of Linus quilts by machine and I always use varigated threads on them. It gives them a little extra touch.