@Mike sais as long as a skin doesnt interrupt the gameplay, doesnt give u any advantage ingame, doesnt brake the game, doesnt affect other players since they see the original skin, skins are allowed. Just like weapons skins or hud skins or sound mods are allowed which are used from most players, even this simple skin is allowed.
for some reasons, Crosshair Mods aren't allowed anymore, so Hud (skins/mods of its kind isnt allowed here) It's not updated on forums which is here since a year (allowed/disallowed modifications) (topic) - something etc on forum, (Hud's Mods. has custom crosshairs and I can't think if kind of other hud's mod could have original crosshair, that's not possible even idk, also for skins mods, I have noidea if its allowed or not, (I heard something on discord, not too much - idk)