I painted my bumper, bumper ends and lower grille a few months ago. I used Krylon Fusion (made to adhere to plastics), no primer or sanding.
So while contemplating getting a black upper grille for mine, last Saturday I decided on a whim to paint the upper grille the same way. I had decided to make the headlight surrounds black. It seems to me - from looking at the underside- that the grille was originally a dark gray.
I'll either leave the emblem black, or paint the letters over with a brush. Maybe some automotive touch-up paint will work, those come with a small brush.