A red veil over a GIMP photo can be the Quick Mask display rather than red image pixels. Quick Mask visualizes a selection, and its overlay color and opacity can be configured. Toggle the mode on a working copy before correcting the photo's color. Turning the overlay off does not automatically cancel the selection it represents.
Distinguish a preview from a color edit
Start with the current document and check whether Quick Mask is active. Compare the same area with the mode enabled and disabled. If the red display disappears while the photograph returns to its previous appearance, that supports a preview-state explanation. If red remains in the image, investigate actual pixel edits or another visible layer instead.
The default display usually covers unselected areas, but its properties can be reversed to cover selected areas. Its color can also be changed. Therefore, neither red itself nor the side of a boundary covered by red reliably identifies the selection without checking the configured mode. Read the setting rather than memorizing one screenshot.
Use a simple test area
This is a reproducible test plan, not a tested output. Preserve the document and use a duplicate. Make a small rectangular selection away from important details, then enable Quick Mask. Record which side of the boundary receives the overlay. Open the Quick Mask properties and confirm whether selected or unselected areas are being masked.
Disable the mode and inspect the selection boundary. Save a separate image copy and reopen it in an ordinary viewer. The goal is to compare a document preview with exported pixels, not to generate a new version of the scene. If the saved file contains the red effect, review layers and edits rather than assuming every red view was Quick Mask.
Keep selection intent after leaving the mode
Quick Mask is useful for inspecting and modifying a selection. Brush work performed there can change the selection instead of adding visible color to the photograph. A user who tries to repaint the sky while still in this mode may be modifying editing scope rather than sky pixels.
Decide whether the selection should remain. If you were using the overlay only to inspect a planned local correction, return to ordinary view and keep the verified selection. If the next operation should affect the whole image, explicitly remove the selection. Merely hiding its display can leave a brush or fill operation restricted.
Accept the document state, not just the export
Acceptance requires three observations: the overlay can be identified as a preview, the exported copy has the intended original colors, and the remaining selection matches the next editing task. A normal-looking export is insufficient if the editor is still set up to modify an unintended area.
Use the same distinction when moving between applications. GIMP's Quick Mask is an external editing mode. Imagild region overlays should be checked using the current product interface; their appearance does not imply identical channel behavior. Preserve an untouched source so that a mistaken preview diagnosis does not erase real color changes.