FOSS gamedev and creative worlds

Every time I put a Mod on Minetest it makes everything in my world bright fluorescent colors but nothing has any type of design. Their are just bright blocks everywhere. Can I fix this, am I doing something wrong?

If a mod attempts to load unknown/unavailable textures, a random color will be used instead.
Are you sure you installed the mod in the right way?

Oh yeah, I saw that when I was devving my code.

It's usually caused by missing .png files, THEY CANNOT BE LIKE .PNG however, with capitals, Minetest, will not read .PNG, but will read .png

well I think that I am doing it right but I guess not. When you get into the Mods folder what do you do then. Nobody ever describes what to do next!