There is a new internal variable called GUI_carColorOverride as of 7.0. I haven't figured out the exact format, but it appears to be four comma delimited values with the first being the hue value from 0 to 359. The last appears to be a saturation value from -100 to 100, and the other two seem to be for reflectiveness and some white.
Seems to require a restart to take effect, so I tinkered with it on my bench until I found some combination that fit my wife's car.
Her car still appears as pearl white in the mobile app.