Canvas size increase leaves tinted areas

[Ofnuts]

(11-29-2023, 11:49 PM)BlueBrick Wrote: When I Increase the size of the canvas, I get a red tinted area that shows the increased size. How do I get rid of that? 
I have included a screenshot 
Mad OS 13.6 Ventura
Gimp 2.10.36
The also happened in 2.10.34

This is because you are in "Quickmask" mode. You get out of it by clicking the button in the bottom left corner of the canvas. 

Now, two facts:

• In quickmask mode, the unselected bits are marked with a red overlay,
  
• The selection is clipped by the canvas: if you do Select > All the selection covers the canvas and only the canvas, outlying parts of layers are not selected. 
  

So, with a full selection, and in quickmask mode, if you increase the canvas, the selection doesn't change, and the parts of the image that were outside of the initial canvas are unselected and get the red overlay.