I have just gotten my first custom and it's a SFS, 55% 1B with 20% Gray.
I guess my two stocks from February of this year had gotten so light/faded, that a fresh 1B seemed shockingly black!! Other than that, the SFS instead of French completely dissappears and I'm EXPOSING HAIRLINE!! Cool as hell to be able to do that.
I did like, due to a combo of fade/Dermmatch, the fact that I didn't have to dye my side/back hair. With this 1B, I definitely had to. So, I'm wodering if a higher gray percentage would do it, or if a #2 color is the way to go?

Picture of a #2 next to a 1B would be great, as well as any 25% or 30% gray.

I actually like showing gray, although I got told 3 times in 4 days that I looked too young to have a 20 yr old kid!

Try some subtle blonde highlights around the perimiter and the top, as well as the hairline - it usually solves this blending problem and distracts the eye away from the blend (if you do the highlights right, it's hard to pick out where the piece hair ends). Try it, you will be amazed with the results! Get a cheap blonde highlighter kit and follow instructions in it. Don't use too much bleach or leave it too long or you will end up looking like a 20 year old kid