Let see, I first did my Guweiz study painting, and while around halfway drawing that I notice a thing or 2 and want to test it on something that I don’t have exact ref of. Mainly something that looks like color correction, how to match 2 or more different object’s light and color. Not sure how to describe it, but I notice similar thing when playing Warframe and turn the color correction setting on. You can see it on the last phase of the painting process. Not sure if the effect is good or not since in Warframe I turn it off, but I like it on my Illustration.
The filter layer I use to do this is overlay, and I make sure to put that on top of other layer but I also make selection tool’s boundary on area that I know shouldn’t get hit much by light. Maybe other people have other method to do something similar, do share your thoughts if you see this 
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Total time is 10 hours in 4 days.
timelapse here,
The Guweiz practice that start this, still long way to go.
I wasn’t sure if the timelapse can help others at first, at least for process reference/comparison, since it has no explanation. But I am glad it actually help some people in some way.