Funnily enough this topic actually came up on the FB a few days ago, actually. Although I am not certain on when exactly striped production ended, but several 1952 units (particularly located in Cleveland, Ohio), featured no stripes and only the base yellow paint.
And, just for fun, here's some photographic evidence of that! (Thank you, Kurt and Luke!)
Wichita, KS:

- IMG_6350.jpg (84.52 KiB) Viewed 5088 times
Cleveland, OH:

- IMG_6351.jpg (64.3 KiB) Viewed 5088 times