Sometimes matching prefinished material can be tricky. Hopefully my following tip will help those using prefinished James Hardie siding and trim.
We are having our homes existing soffit, fasia and gutters painted to match our new James Hardie ColorPlus (prefinished) trim. To obtain a perfect color match all our painter had to do was to provide the exact name of the James Hardie color to our local Sherwin Williams store. The Sherwin Williams data system cross referenced the color to a formula. The resulting Super Paint was a perfect match. Our painter also recommended taking along a sample of the Colorplus finished material and the small bottle of touch up paint provided by the James Hardie contractor as an additional way to ensure a perfect match. This applies to all James Hardie products prefinished using their ColorPlus Technoloy. Btw, our trim is "Arctic White" and lap siding "Light Mist" (light gray). I am not affiliated with either James Hardie or Sherwin Williams.