On my Deep Wedgewood Blue truck, Satin Black Krylon Fusion was FAR too shiny. While Fusion Flat Black looked more proper, but was too gray looking. I later did Dupli-Color Truck Bed Coating(aka bedliner in a rattle can) and it looked proper on the truck.
Best bet is to buy some products and see how they look on a scrap flare or scrap chunk of plastic to see what you like best. Always remove the piece from the truck before coating it to see what looks best to your own eyes.
I've grown to the SEM Trim Black product for it's perfect middle ground between Satin and Flat....and it's long lasting characteristics. Straight up OEM like black.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.