I color.
When I was young and had only a few gray hairs, I'd pluck them out. (I have thick hair, so plucking actually helped matters.) By my late 30s, I had enough gray to not want to keep plucking, so I started coloring.
Now, at 50, I have lots of gray in certain parts and almost none in other parts. When I color it, the gray strands make the inexpensive Revlon ($3) dye look not so monotone because they remain a tinge lighter than the still-dark-brown hair.
Bella Boo posted that it can look obvious and artificial and montone, but I think that is mostly because people leave the color in too long. It so coats the hair that you lose the translucency that makes it look natural. The flip side is that not all of the gray might be covered, but I don't mind a few strands of gray showing.
And frankly, I'd rather look obviously dyed than gray. There are ways of doing it well.
There's supposed to be a touch-up product out there. I've seen coupons for it, but I've never seen it in the stores.
I'll go gray when I'm 70 - if I live so long.