I meant to do just that with mine this grow, but somehow it got overlooked. It doesn't SEEM to be making a dif, but then, how would I know? I WILL paint the outsides black after this grow for sure. It might not make a dif, but it sure can't hurt.
MY concern with those pots you have is the Height to width ratio. My first grow I used square 4 gal buckets that were tall and relatively narrow like yours. The problem I ran into was trying to judge soil moisture content. The top of the pots would be dry, but the lower 1/2 would still be wet. I believe that was a big factor in my over watering my first grow. (Of course, overfeeding and nute burn didn't help either)
I am using low wide pots this time, 5 gal buckets. I'd LOVE to find some short, wide 10 gal buckets from somewhere.