[The_bluester (Paul)]

A trick with APP, I assume you are using the background and star colour calibration tools? I find the star colour calibration to be inclined to cause a green cast. But recently I read up on the background calibration tool, that tool attempts to make whatever you have defined for it as containing background, grey. If there is nebulosity over the area it will make that grey and throw your colours off.

Before selecting areas for the background calibration tool, apply the highest stretch preset to the data, which will look terrible but highlight the best areas for you to select as containing background, then you can reduce the stretch again. It might be tricky in that field as there might not be much space available that does not have nebulosity in it.