[Sunred]

So one tidbit that was mentioned in the Terebi-kun scans was that Pink is a genius when it comes to driving, and so currently my speculation is that Red is the mechanic of the group and Pink is their designated driver.
Now, Blue's occupation still seems unclear, but my primary guess is he could be the designer of the group like Naoki/Blue Racer but has the attitude of Touma aka Lupin Blue since it doesn't mention him being skilled in driving. Other than that, I was thinking maybe he joins the team while passing by and trying to rescue Red and Pink from the Hashiriyan attacking them, and he becomes part of the crew when he is chosen as a ranger because of his professionalism and he considers fighting the Hashiriyan a challenge.