In the virtual garage it's possible to change a vehicle's colour, where previously there was a different vehicle for every colour variation.
Of the 54 different weapons in Arma 3, 23 are just coloured variants (these include Marksmen DLC weapons). I suggest replacing all coloured variants with a 'colour' attachment slot.

Generally attachment slots can be left empty, so I suggest making each weapon by itself black, and adding an attachment for each colour besides black.