What would happen if IMCDb had carriages too? As in horse-drawn ones, not train carriages. I've just watched a film and the carriages are making me think about asking this question
Brands like Robinson & Cook and their models will finally be classed as a vehicle, even if their horsepowers are 1 (literally)

Well , if what i saw in Lucky Luke is true , you can at least go to 4 horsepower...

One of the criterias is the vehicle has to be able to move under its own power .. or at least was able to once it has left the assembly plant for the junked / burned / crashed ones so carriages are very unlikely to happen

So if I wanted this, I'd have to make my own website?

Yes, because it won't be added here.
And I have doubt these would be easy to identify with make & models, that's not as commonly known and recognizable as vehicle makes & models.

We have enough trouble identifying older (pre-1932) cars because many looked alike and all people who directly associate them are either dead or belong to so niche circles that they specialise in one particular brand of car only. Horse carriages are even more niche and I doubt many car people associate with them anyway.

So imagine the futility in this predicament.

If I were to make my own one, would it be treated as an official DLC sort of thing to IMCDb?

For what's worth here are some of the carriages posted at https://imcdb.org/movie_90481-Matlock.html#Comment2435494

Sorry Antoine for asking too many questions, but what about adding colours? Some cars don't have years (partly due to there being barely any changes or disputes), so this is going to be like years basically. I'd prefer codes (like Z168 and not Metro Blue) but I don't mind, whichever works best for you

What do you mean? Store the color codes of the car? We already have a lot of work with just identification, adding too much info will make it even more difficult to maintain.
You can put color info in the comments (though that it does not allow to search on it, but I don't know if such feature would be used a lot anyway).

I thought this wouldn't work out for car in the darkness, so it was just a 'What If IMCDb had colours?'

I guess I'm now going to start to add colours