All you need is the single file autotint.rpy. Just read through the comments, maybe delete the sample bits at the top, drop it in your game and use as advised.
Using Ren'Py 7.4 matrixcolor to provide a smooth (over duration) tint of displayables.
This is a pretty basic piece of code which allows for separating the tint (or tints) from the images using them as well as providing a smooth dissolve like transition from one tint to the next.
It is mostly aimed at situations where a developer wants to subtely tint their sprites and/or backgrounds to show changes in the time of day. For example:
default day_period_tint = TintData()
label badger_house_evening:
scene bg badgerhouse at autotint(day_period_tint)
show badger at autotint(day_period_tint):
align (0.5, 1.0)
badger "Looks like evening is setting in"
$ day_period_tint.set("#43A")
badger "Yup, definitely evening as everything has gone rather blue"
badger "It's almost too dark to find the light switch. Eek"The notes in the rpy file should pretty much cover how the system is used.
If you just want various layers tinted (hair, skin, clothes etc) you would likely do better just using a matrixcolor TintMatrix directly rather than this fading in one.
Smooth fading during rollback and rollforward is disabled in favour of just instant tinting (which works better in those areas)
Sprite used in example image: https://www.deviantart.com/kid-blue/art/female-teacher-1-274513797