problem with set color to alpha

[Jeanne]

(02-02-2019, 01:35 AM)rickk Wrote: New to all of this, Perhaps I am trying to go about this the wrong way.....not sure.
But, for instance,  suppose I wanted to cut an image of somebody  out of picture "A", and insert it into an already existing image "B"

SO, I painstakingly draw a white area  all around the perimeter of the desired target image, then extend that white area sufficiently large that I can select and crop to a rectangular  image for use.
Then I review the image and find a color not in use in the  target image, say  HTML color h1cf905 for  example ....no sign of that color anywhere in the target image , and then change the white area surrounding the target to that color, and then set that color to alpha.


Hoping to paste that image, complete with the transparent surround, into the "B" image.
Except when I set the surround color to alpha, it's causing the colors in the target image to get all whacked out.  For instance  with the  color mentioned  set to alpha, everything is shifting into violet colors.

Almost seems like the "color to alpha" function isn't discriminating properly, and is perhaps shifting all greens to alpha?
Thanks in advance for pointing me in the right direction

Found your problem thread searching for the same solution as you .  
Tried the suggestions - was rather cumbersome. 
Finally solved the problem by adding an "Alpha Channel" to the image.  {Layer >Transparency >Add Alpha Channel}
(If you are working with multiple layers, you'll need to add the Alpha Channel to the specific layer you wish to edit.)
I made sure I did not have open lines to other areas in the image containing similar colour as my background.  Background happened to be white.  Once that was done, I used the Fuzzy Select Tool on the background, then chose "Colour to Alpha".  {Colours >Colour to Alpha}
Worked like a dream.  The "Select by Colour" tool is a bit different - it will change every piece of the colour you picked to Alpha.  Of course - you can also adjust the Threshold on either colour picker tool to ensure you have less chances of grabbing reds as well, if you only want a pink back ground erased.

Really posting my little story for others looking for a quick solution.  Hope this helps!