TL;DR Considering that the styles were more accurately "DOS styles palette-swapped to imitate Genesis", feel free to adjust the colors as you see fit.
More background:
First, keep in mind that the so-called Genesis styles were not direct ports of the actual styles in Genesis at all. (If they were, some of the terrain graphics would've been actually different besides color, as compare to DOS.) In fact, had I been lazier I could've never bothered with them. The primary goal at the time is to make the Genesis-specific levels accessible to users of DOS Lemmings, CustLemm and Lemmix, rather than them having to hunt down an emulator and ROM. It is obviously not going to be the exact same experience as on the Genesis, since even the game physics already has minor differences (or in some cases not so minor, like the timer-speed difference affecting levels like "Just a Minute", or the fact that Genesis's level area is 512 pixels wide rather than DOS's ~1600). So the idea is that the purists who wanted an absolutely authentic experience would've just used an emulator already, and for the rest, they would prefer just needing to get some level files in order to experience something very close to the Genesis levels, without having to set up anything else. And so indeed, you can play my converted Genesis levels with DOS styles--the levels are basically set up for using the unmodified DOS styles that come with DOS Lemmings/CustLemm/Lemmix.
I did recognize however that even though the graphics and gameplay between DOS and Genesis are nearly (but not actually) identical, the Genesis version uses different shades of colors than DOS--a difference that is decidedly not minor in that it affects every visible element in every single level. But since DOS styles uses a palette stored separately from the actual graphics to assign the actual colors used, it would take relatively little effort on my part to create basically palette-swapped versions of the DOS styles by simply modifying a few entries in the GROUNDxO.dat files while leaving the actual graphics in VGAGR files intact, and then you would get the Genesis colors on DOS styles. And I figure seeing the Genesis colors may be compelling enough for some people that they would take the extra minor effort to setup those extra style files so the levels look "more like Genesis" in the most noticeable way. And
that was the origin of those "Genesis styles". Perhaps a more accurate name would be "DOS styles palette-swapped to imitate Genesis" but that doesn't quite roll off the tongue as smoothly.
DOS Lemmings/Custlemm/Lemmix style data (ie. the GROUNDxO.dat files where actual color information are stored) do not support changing the background color at all. So even though I can clearly see the Genesis uses a dark tint of blue for the background, there is nothing I can do to support that particular color change. There is a possibility that at the time I considered it more preferable for Crystal's darkest non-background color to match the background color, like it was the case on the actual Genesis (perhaps so that things that were not readily visible don't suddenly become more visible, or something like that--keep in mind that the colors can potentially be used in interactive objects and animations as well). So while I don't specifically remember doing so, it is conceivable that I purposely left the darkest terrain color black in order to match the immutable black background you are forced to use in DOS Lemmings/CustLemm/Lemmix. The other explanation is a simple oversight on my part.
One other thing: IIRC colors are stored as 18-bit values (6 bits per RGB component) in DOS/CustLemm/Lemmix GROUNDxO.dat files [because the actual hardware at the time of DOS Lemmings only support that many bits per RGB component for palette colors]. Most computers at the time of the "Genesis styles" (and nowadays) represent colors using 8 bits per RGB component. I don't remember anymore, but do believe I simply used screenshots from the emulator to get the colors to use, but it will then still have to go through an 8-bit to 6-bit conversion in order to specify the color in the GROUNDxO.dat files. So in terms of 8-bit RGB component values when those 6-bit values in GROUNDxO are eventually up-converted back by Lemmix/DOSBox etc. for display on PC, they may end up slightly off from the values you get from the emulator, but should be by no more than 3 per component (since 2 bits map to 4 distinct values). This obviously cannot explain away the difference of 33 for the darkest non-background Crystal color, so for that particular difference, it was either intentional or an oversight as mentioned earlier.
With the new update to NeoLemmix allowing background colors, it was brought to my attention that, for gameplay reasons, the background color of the Crystal set should be changed to avoid things being the same color.
That's the thing, it was well-known that the Crystal set (both in DOS as well as Genesis) used identical color for the darkest terrain color and the background color, and I even seem to recall at least one actual custom DOS level (or if not, then at least proposal of such a level) explicitly making use of that fact to create evil invisible terrain, for better or worse.
I can perfectly understand the proposal to purposely deviate from actual DOS or Genesis in this regard. But at least for the purposes involved at the time, there's a chance I might have specifically chosen to preserve this property of the Crystal set.
Upon a bit more research, I can quickly verify that the emulate-and-then-extract-colors-from-a-screenshot method is probably not the best way to go about doing things, since I was able to get different results simply by tweaking the emulator settings slightly.
That seems a little suspect. Which settings are they exactly and what emulator are you using? It is possible the settings were provided only as workarounds for certain games that they weren't able to perfectly emulate resulting in undesired colors. I don't remember what emulator I used but I did not change any color-related settings from the default, and I think I also cross-verified a few colors with screenshots of Genesis levels on
www.deveria.com (now defunct but you can use archive.org wayback machine to look it up). Granted, the screenshots from
www.deveria.com are likely taken from an emulator left at default settings as well.
Besides the background color and Crystal's darkest non-background color, what other color discrepencies did you find? I would not have expected any other major color discrepencies (at least relative to an emulator running on a PC) besides those two.