Vinyl siding does not really come in dark gray. Deeper colors in vinyl siding are going to be teal, forest or mossy greens. You can use paint formulated for vinyl, but vinyl doesn't do well with heat, so when it is a dark color and gathers heat, it doesn't perform as well. I can't recommend vinyl siding for most jobs because it is really cheap and looks it and doesn't last. If you are siding a house, it will need to last a long time, and you don't do yourself any favors to put something that won't last on the house. . . hardie does have good dark colors and a much higher quality product. Check out the options at your home store before you go vinyl. It has hidden costs.