what is more popular silver or black face plates

I have both. I don't really have a preference. I think some components look better in black and some silver.  My dac, ddc, clock, and phono stage are silver. Everything else is black. 

I purchase a fair number of used components, so I have given up being that picky.

That being said, I find myself grouping them by colour on the rack.

I prefer black, but if I'm getting a great deal on silver faced piece, I don't care...

I prefer black.  When shopping for used gear, I've unfortunately seen silver to be consistently a bit cheaper used.  So I assume there is more demand for black. Jerry

On tube, gear clearly black as it provides more contrast to the tube glow. For the rest, typically there is no choice. I may prefer silver slightly as dust is less visible on it.