The technology hasn't caught up to Starlight Xpress! Most 3rd party programs cannot handle colour FITS files. It is best to use copy and paste. With photoshop all RGB channels are retained for further colour processing if you desire.

How to do it: Pull down the "Edit" menu and click on "Copy to Clipboard". Then bring up your favourite bitmap editing program and use the "Edit" menu there to "Paste" the image into that program.