1) Perhaps you're using D.colorSpace(COLOR_SPACE_SRGB) ?
I recommend D.colorSpace(COLOR_SPACE_DCI_P3) to increase saturation (I'm using this for my own game)
2) D.bloomSat was removed, which may decrease saturation if you had it enabled, you can try restoring it here:
https://github.com/Esenthel/EsenthelEngi...r.cpp#L277
replace
"!D._bloom_cut" -> "true"
But I don't recommend it as this saturation was by mistake and inaccurate.
3) PBR adds some highlights/reflections which decrease saturation, lowering material "reflectivity" from 0.04 to 0 will increase saturation, however disable reflections and make things not physically correct.
4) If you disable cel-shading the colors get better?
I'll do some tests about cel shade shadow that you're mentioning tomorrow.