I suggest you try it out on a sample and see if you are getting any bobbin thread on the top. I just completed a quilt that I changed thread colors twice on the top but used the same bobbin thread throughout. I could see the bobbin thread a couple times, but it was not noticeable. Sometimes I have more trouble than others, so for me , its a choice I make on each quilt-and sometimes each thread color change. I DO try to match the weight of both top and bottom so there is not TOO Much difference. I ALWAYS try a bit on the side right before I start for the day. EVEN if I have had no problems the night before. Ask me how I know!( PS you can always change the bobbin thread if you do get gold thread on the top. if you look at BIG name quilters, you can see diff bobbin colors on the back...)