Did you pick the corn silk because of the color of your backing?
I think it would be fine as you said you don't want to change thread colors. It floats on the blue and isn't really popping out - which I think is a good thing. I'm not a fan of thread showing on background fabrics (but that's just me). I think the corn silk will give the blue a nice sheen.
That said, I don't think the problem is the thread color. I think you really need to pull out all the stitching you've done already and solve the tension problems that were mentioned by previous posters.
The good news is that it shouldn't be that much of a hassle - clip a stitch at each end of a fan row on the front and pull the thread. It should come straight out, and the back thread should also just pull out. There's nothing really holding it there as the tension is so loose.
Make a sandwich and figure out what the problem is. Are you FMQ-ing the fans, or using a walking foot?
I would suggest the walking foot. Yes, a lot of stopping and turning, but your stitches will then sink into the quilt top (instead of laying on top of them), and will be much less noticeable.
Also, you might want to mark some lines, or at least use the walking foot to gauge distances so the Bfans can be more consistent. If you're comfortable enough with FMQ-ing, I'd still mark some of the lines.
I think all the above will totally minimize a lot of the visual issues you have with color of the thread.