Just to mention, two more really great uses for this:
- help people that are colorblind. If the unit colors look similar, an option to adjust per-country hue so they can be visible would be excellent. Flags would help this, I'm sure using colors that look physically different would be even better.
- building on maps that have many nations. If for example someone wanted to mod a map that has many nations, like NWO, or anything with 10 nations+, adding a new unit is a bit of a nightmare. You have to use color-picker very well to match the existing hue and it's hard to say if the new units will still look cohesive. For example, add cavalry and heavy cavalry, that is perhaps 20 units images and for each you need to do a really great match of existing hue for it not to look just hacked on.
@Cernel I suspect the usage of this feature would be opt-in per map, or could be used as a fallback when unit images are missing. It wouldn't be the case that we'd go through all existing maps an delete units images to leave just the auto-colorized ones.
This would I think end up being the primary use of the feature. If it helps map makers in the process that's great, but I saw it as something that the average end user would find useful, either as a visual aid (if they are colorblind or are having difficulty distinguishing units for whatever reason) or just purely based on aesthetic preference. Maybe someone wants to sub out purple units for some other color, using this system you could do it on the fly. Currently its very easy to modify a nation's territory color via hex code in the map properties file, but if you wanted to change the associated units, that is more laborious and requires an outside image editing application like Gimp or PS. This might be easy for a map maker, but rather more involved for the average user.
Instead of trying to arbitrate people's individual tastes by coming up with a default unit set that everyone must adopt, this gives players the freedom to color the map/units in a way that suites their personal preferences, without requiring much legwork or stepping on anyone else's toes while you're at it, since it'd basically be a local setting.