Hey mate, I stencil spray paint for art and sell my paintings so this is my 2c ;)
I think it looks too moo-cow-ee because there needs to be another colour (darker than your grey mid tone, but not black) to break up the contrast between the white and black. Maybe just another grey would look good. Look up Montana Gold Spray Paints, theres like 20 different greys, and they dry super-quick! rrp about $14 a can, pricey but I stand by them! All my last years works were 95% white, black and grey tones so I had alot of trial and error, so you can learn from MY failures haha.
toby