It is actually a photo of a church (portrait)where the sky is almost white and I wish to change the sky to blue
To the best of my knowledge, I don't think Qimage can paint a selected area.
In Select Color, use the eye dropper on the sky and see what color "row" Qimage indicates in the grid.
If it is blue or cyan, we can darken the blue either with Select color or some Saturation of blue.
If the eye dropper shows Neutral, (bottom row) then cannot change it.
Fred