Select pixels in Paint tab by elements

[Cubouse]

Detailed description of your suggestion

When the model has as disorganized UV, and different elements share the same colors in the texture, it is time consuming to select the colors from only one part of the model to edit them (using the paint bucket tool, do curve adjustments...).

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Let's say, a cliff and a bird both have shades of grey/white:

And I wish to use the brightness & Contrast curve on only the white parts of the cliff, to darken them.

I can select by "Same Color" with the Selection tool in the Paint tab, but that selects both the pixels of the cliff and the bird.
And since the UV map is disorganized, I cannot tell easily what islands I should subtract from the selection to only end up with pixels from the cliff.

To make the process easy, I wish there was a tool much like the "Selection Tool", but for elements.

This way, I could subtract from that selection the elements of the bird (by clicking the 3D elements in the viewport one by one, or in the outliner to click the bird group and select all of them at once).

Or the other way around, I could select the pixels of the cliff by clicking the elements, then subtract from the selection the green pixels of the grass with the the Selection tool with the "Same color" mode.

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I think this would fit well in the sub-menu of the Selection tool, it is essential that it could be used with the different selection operations modes:

Additionally, there could be a "Face" mode, to select individual faces rather than the whole element.

Maybe even a "UV island" mode.