Well, not really red paint. This is a shot from sometime in the 1950s and the red-colored dome is covered in primer. We came across this photo thanks to a Twitter exchange between @darsal and @MrTinDC.
A Closer Look at the Red-Colored Dome of the Capitol Building in the 1950s
Mmmmm. Red lead!
I'm still hunting for the one where I first learned of the strangely colored Capitol dome. I believe the setting was Pennsylvania Ave NW between 2nd & 3rd. The subject was two people, man and woman, posing in front of a streetcar with the dome in the background. I'm not sure the Capitol was even mentioned in the caption, but the colors were definitely not.