So I have masked out the grass and top of the trees with an ID mask so I could adjust the colors post render. The problem I am having is I can make each color adjustment independently and everything looks correct. The problem when I go to combine the color changes into an single image. Combine grass color change and the tree color change. I am using a mix node, and I have tried every option, add, multiply, mix, color, etc…
Color changes are done on one single source, using mask as fac. Do the adjustments serially, not in parallel. Do not combine the separate color adjustments with Mix node, it does not work due to the way different mixing modes operate.
They can be done in parallel, but to combine them you would have to copy the modified area onto original source using mask as fac. As there is no copy or keymix op in Blender you must set alpha first, then do an alphaover.
If there is transparency in source (which you seem to have as sky is black), you should unpremult the image before color adjustments and premult again after that to get accurate colors on semitransparent areas.
