Black hands down. To block out the heat.
I have 3 vents in my RV and they are all black.
One blew off in a storm and the mobile RV did an emergency replacement with a white one. I forgot about and a month later was walking thru the coach and all of a sudden I felt a blast of hot heat on my back......I was walking underneath the "white" vent cover! Color does make a difference.
DW doesn't have to pull out the sewing machine for a cover, pick up one of these RV vent pillows at any camping store. Sticks right in the vent opening. No messy velcro tabs to stick up all over your RV. Makes a big difference in keeping the heat and cold out. And it will also keep the light out too if that's a plus for you.
