problem with set color to alpha

[akovia]

(02-03-2019, 08:06 PM)rich2005 Wrote: There is a color erase but the same problem as before, in an RGB image you can remove elements of the 'erase' color but liable to leave remnants of the rest behind.

I use color erase quite a bit and found you can use the curves tool to clean up the remnants. 
This tut is a bit old but it still works.
https://youtu.be/N1B0TpyZ0vs?t=1595