Nice new variation on that skin, but some things could need a make-over. All are personal suggestions and don't necessarily need to be changed.
I personally find the mod icons hard to read. The contrast is too low between the two colors.
To the mod icons on all versions: I don't really like the colour categorization into vertical lines instead of horizontal lines. With the horizontal lines you can display the difficulty level of the mods (easy/harder/unranked) additionally to the information at the left more clearly like that.
The hitscores are too dark to be noticed due to the gradient going to black at the bottom.
I also strongly dislike your standard spinnerspin.wav. This high squarish saw sound is rather annoying.
The other thing is the thickness of the hitcircleoverlay. It is 14 pixel (the HD one) wide between outer and inner border. Due to this a part of the slider shows beneath the inner edge. I would make it 16 pixel wide to hide the sliderborder completely behind the overlay. This wasn't noticable since your old hitcircle went all the way to the edge and hid the sliderborder.
Last is a personal review on all versions up to Fluorescence:
I wasn't really there in the beginnings of the skin, but it made a long way comparing all the old versions. I was hooked on this after the HD release that made this skin an true original one. I liked the non-intrusive color scheme being easy on the eyes and considered it making a skin I would play with often. Having worse skill than now I dropped it because it was somehow difficult to read on. I just later really read the text and liked the concept at first. It is nice seeing a skin themed with so much research and thought going into it. But with the following Planckian Locus update it became more unreadable for me.
With this update I came to a conclusion; your skins are very hard to read for me and don't really fit into my gameplay completely. Your UI was always eye catching but the gameplay is rather distracting after the Pl. Locus update, atleast for standard mode.
I for myself also like to play with a cursortrail and always found it missing in the extras since you also provided followpoints as additional elements. Also hitscores in a plain colour without the gradient would have been a nice addition.
The personally best looking version would be the standard version of your skin with some brighter colours for the combos with maybe your circle design for Fluorescence.
In short: Standard is great and easier to play, after Locus it went too crazy for me personally.
Most of my previous posts on here were rather help on fixes and not really judging comments, so with this update it was time for that.
This is a great project you worked on with detailed reasoning behind your design choices which lead to the success of this skin series.
Let this success grow even more.