Ability to change gamma, color saturation etc to HiPS layers

[Atque]

In the Aladin Lite viewer, users have the ability to change gamma, saturation, opacity and even changing the color maps of the HiPS layers. If there are no legal issues, Stellarium might want to implement similar manipulation possibilities.

[github-actions[bot]]

Hello @Atque!

Thank you for suggesting this feature.

[gzotti]

See also #1324, #3314. I'd like to be able to combine 3 B/W surveys to a colored one, in addition.

[Atque]

Perhaps also adding atmospheric extinction, just like for TOAST. For example, the Mellinger survey would look better with extinction and fading in and out with twilight.