Caltrain cars not painted

Odd question but why are the Caltrain Bilevel cars not all painted. I see plenty of bilevel not painted.

Regular steel rusts quickly and needs to be painted to prevent rust. Stainless steel doesn’t rust quickly and does not need to be painted to prevent rust. Many of Caltrain cars are made with stainless steel, that’s why they are not painted.

I should get some pictures. In this picture, Here The second caltrain car isn't painted red and instead blue and white. It looks almost like it came from the factory. Is there a reason for this?

Not aware of any car swapping between Metrolink (SCAX)and Caltrain(JPBX),all the BBD "Sausage" cars are painted from the factory
Second car might be leased from Metrolink(SCAX)

Caltrain has purchased several cars from Metrolink, who no longer allows them to lead for collision fears. That car is still in Metrolink colors.

Those are Bombardier built BiLevel cars which use regular steel, therefore all of them are painted to prevent rust. The second car in the photo was originally used by Metrolink in Southern California, and is still painted in Metrolink livery - with Metrolink's text and logo removed. Eventually those cars will get repainted, by whomever buys them, when Caltrain's new Stadler built BiLevel EMUs enter service, or if they last a little longer, when Caltrain retires them. Which might explain why Caltrain hasn't repainted that one in the wrong livery yet.

You all are awesome! Thank you very much.