This is gonna sound so silly but I found this decent jacket for a specific outfit in mind but it doesnt come in maroon (one on top left) and i couldnt find one with the color i want, could i like just paint it maroon?
Paint would come off. Usually dye is the way to go. You need a certain type of dye which does polyester and works at high temps. As most clothing nowadays use polyester threads
Dying clothes a darker colour is easier than dark (black) to something else. I.e. finding a light grey cotton denim (?) jacket would likely work out better