I recently got a Gretsch Singerland Bass, snare, hi-hat, and crash jazz set.
Congrats on picking up some great old drums!
...but there's nothing Gretsch about that drum. Gretsch and Slingerland were two completely separate companies when your drums were built.
It had a marble/pearl finish that became warped into a yellowish color. I was wondering what I could do to get the original color back.
That finish is called White Marine Pearl. You can polish it up and it'll look great, but the yellowing isn't just on the surface so you won't be able to get it back to its original color.
In case you're curious about the age of your drums... The stamped "dog tag" badge on your drum came into use in 1953. The style of lugs on your drum were replaced by "Sound King" lugs in 1955.
Your drums are a really close relative of my own. I have a 1955-56 kit with that exact same badge and finish.