Clone problems colour doesn't match the source

[denzjos]

Not really an answer to the cloning question, but there are also other solutions to delete things in a photo. It depends on the situation. A few examples: the heal filter (Filters / Enhance / Heal selection) or copy part of the photo and scale it in one direction as shown in the example (Tools / Transform tools / Scale). Then 'New from visible' to blend the copied part into the photo. Use the Healing Tool in case of color boundary errors.