Matching wood stain to paintable plastic
The best way to match it is to remove a small piece of the siding and take it to any paint store that offers computerized color match. I/E: A piece of window trim, a loose knot hole, or use a painters 5-way tool to chisel out a very small piece from the bottom of a corner board or other inconspicuous place. Also, you might try calling a local paint distributor like Sherwin-Williams. Tell them you are considering some paint upgrades and you would like them to come out and match up the color with a fan-deck so you can weigh your options. If they think there will be a big future paint sale at stake, they will send out one of their road reps to speak with you and match the color. Remember to use a primer on that plastic before you paint it.