In case that it may be useful, posting some of my prev experience here.
One thing I noticed when I looked at how pheobus evolved his tileset is that his evolution path actually coincide with mine at many stages. So I thought I'll post some of my decisions and rationale to see if it can help, as a reference hopefully helpful as an example or counter-example.
Regarding ground tile:I tried the "solid" ground before. In fact, it was one of my earliest change. My chief reason is that I want to be able to tell solid ground from a channeled tile easily (I think this could be phoebus's reason as well). But due to the fact that most other tiles have dark background, it will appear ugly and disruptive. I briefly tried to "add background" to other tiles approach, but I did not like the way it turns out. also, background region is often used for other special indicators e.g. brown when prone, red when bloody etc. And adding a background to other tiles is also destructive in nature (hard to get tile when clean background back since we are not using a multi-layer file format). For this reason, I tried to fall back to dithering and reducing the intensity of "ground" tiles (again, same as phoebus, I was actually quite amazed and amused when I find our thinking and evolution coincides). Again, it only reduces "tear" between ground and other creature/objects.
It is then I decided that ground will simply have to have a "natural" color of black since there are countless other cases that cannot be resolved satisfactory given the limitations of the gfx part then (no transparency back then). So instead of making the other tile matching ground tile (by dithering other tile's background") I decided to make ground tile match the color black, at least around the edge. In the end, I chose a light noise pattern, which will be somewhat recognizable as ground, but will play nice with other tiles in black background. It DOES have the original problem of hard to recognize ground from channel, but not as bad as before (recognizable with a little attention) and have a more even feel for both above and underground ground. Also plays nicer when the game decides to use an inverse tile (reversing the opacity)
This is a screenshot made for different purpose posted a while back, but I think it can serve adequately as an example:
Regarding tile used by text:Initially, my main purpose in modding both 437 tileset and gfx tilesets is to make play a little more informative and intuitive (for creatures, gfx tileset actually shows MORE information, e.g. able to tell woodcutter from carpenter), but at some point, I fell into the trap of wanting to "make everything gfx", where i then proceed to try to gfx-size all the tiles in 437. The immediate result is that text becomes hard to read. so much so at at some point, I realised that, the game is actually HARDER to play. I then proceed to undo many of my changes and the immediate aim is to preserve all text (and punctuation). I was only able to do it partially. the basic alphanumeric is ok, but the accented char are used in names etc. I had to do a "accent removal" mod to the language files to get rid of them, and it becomes a lot better. Personally, I am a proponent for "preserve text". Well, there ARE a few compromises I have to make, like the "O" which was rigged to join up properly with walls, and "0" to have an outline that suggests that it is a coffin etc. There are a few funny cases in punctuations too.. e.g. =, <, > have been partially gfx-sized but retains their basic symbol hopefully recognizable. ";, which are used for ground patterns gets a VERY LIGHT noise noise dither that is filterable by brain (at least mine) when used in text. the channel designation tile, or underscore, gets a black background shovel symbol which only shows up when used in reversed (as in case of channel designation) so will appear as underscore normally in black background text. (luckily, I haven;t really seen it used in text in reversed). well, the list is incomplete but i think it shows the ideas. The thing is: I realised that full-gfx just isn't possible until maybe the presentation arc get started. So I compromised with what I'll call a "half-gfx" set which serves to help/improve gameplay.
Regarding changes to raws:when a tile modder deals with limitations of 437 enough, he/she will turn to this at least once in their modding life-span (if you haven't hit this dilemma, you prob have not done enough tile modding). It may come to certain point that the only way to remove certain ambiguity in the way the game uses the 437 tilepage or to be able to introduce more recognizable tiles to certain creatures/plants is to mod the raws to use a different tile. But I personally find this firstly to be tiresome especially during version upgrades, and some people dislike tampered raws, of which there are the pure gamers who just want to play the original game (this group can be pacified with a pre-packaged, pre-modded installer/game) and the partial modders (people who make their own small changes to raws, who finds it troublesome to try to merge changes from different sources). I can't speak for the masses (maybe Pheobus should setup a poll for his set to see how many people prefers untampered raws), but I personally don't like tampered raws (Not that I don't play with changed raws: I am maintaining my own small changes, which included removed accents from language files, and gender-specific names for domestic animals). My advice to pheobus would be to perhaps provide an "untampered raw" version of the 437 tileset for people who like it so?
long post, hope i have not worn out reader's patience. Why I write this, is just that I hope that it helps. If it doesn't, then please ignore it.
regards.