Ziz said:

If Ady or someone really wants to focus on the ship stripe colors then do it for the same reason that Vader's TIE has bent wings - so that the audience can easily remember which character is in which ship. Originally, Vader was going to be flying a regular TIE just like his wingmen until someone suggested his should be different to make it easier for the audience. Apply the same logic to the speeders - Luke's should have the orange stripes so it stands out as him being the squad leader. Everyone else has gray or no stripes.

Or the other way round....Lukes being grey markings and his colleagues orange....only thing being they applied this logic after live action had been filmed....:(