Depending on how fussy you want to be, or if you might want to paint
a bigger area at some point, I had pretty good luck mixing 2 different colors of Nason acrylic enamel.... neither was quite right on their own, but mixed 50/50, the combination is very close to the original gelcoat color.
My CT-13 was hit from behind, so I had a lot of fiberglass repair to do, and then had to repaint at least that portion of the interior. So I painted out to where the f/g curved, or met a window molding, etc..... and then carefully buffed the edges once it had cured for several days, and it came out pretty good. [and this enamel is pretty affordable stuff--my initial try was 2 half-pints mixed up, with some reducer bought for it as well, for $30-40
One of the Rustoleum off-whites comes pretty close, as well, if you don't want this more complicated approach.