I recently thought about ways to make Daggerfall/DaggerXL look less monotonous. One idea I came up with was some kind of texture generation, based on a default texture.
So there is a default stone texture that can be changed in size and color palette (maybe it could be deformed, too). While dungeons in the mountains could have a more grey/green color and a larger scale (rocks), dungeons in the desert could have a yellow color to make it look like sandstone.
All the generation process is done in-game, so there is no need to have a texture for every varation.
This could be done up to a point where each house/dungeon has a differnt color scheme.

Like Minecraft's grass in different biomes?
The texture is black and white but it gets tinted with a pallete depending on what biome it's in.

Yes, just like this
Just with more parameters to change the texture.

Daggerfall already uses different texture sets based on regions. The desert dungeons do have a sandy colour compared with the grey of the mountain dungeons. This even applies to cities. The buildings in different regions have different textures. Some of them look quite ridiculous. The mountain areas where the houses have blue interiors are quite ugly imo.

The trick with any kind of texture generation is you'd want it to stay consistent so places keep their sense of being a specific place rather than just being a location that was generated for a certain quest. It works well with Minecraft because the map is generated once per game rather than once to keep forever.

What I wanted to be implemented is texture variation based on a single texture. In vanilla Daggerfall there are sandy textures, stone textures.. etc., but it would be an improvement to have brighter/darker sand/stone textures (variation within a texture zone) to give every single house a different look. The information about the texture variation could be stored in a "heighmap"-similar picture. For each dot on the ingame map there is a certain color set which influences the variation (as a seed for the generator).

It certainly is possible and I'm sure it won't be hard to implement.

Gray-scaling the textures and applying a tint most certainly would work. However, if you want to take it a step farther, you could, oh, idk, maybe Red/Blue/Green-scale parts of the texture, and have a script to change the color of the those colors.

For example, let's say you have a tile floor texture with a checkered pattern on it with four squares. Two of them are in gray, two of them are red. You could have a script of some sort to tell the gray ones to be brown and the red ones to be white. And if you didn't set any limitations, you could have a neon green/ hot pink tile floor! Who doesn't want that?!

Idk, just a thought.