Hi Dave,  That's something really useful in APP which by my not using it I didn't know about. One more thing that would make it an attractive proposition to me. However whilst still trying to learn more about PixInsight I don't think my brain would cope just now. Thanks for posting that as it shows what each combination will produce, and that's a good thing to know and useful.  Keep well  Ray 

Thanks Ray.  In APP 'combine RGB' the formula is selected and the appropriate stacks loaded.  The formula apportions % colour against the various filters - really slick solution.  Dave