Ponibooru

Anonymous@1347058 said:
Chocolate syrup is when she's being lubricated
Frosting when she cums
Hot cocoa (not extremely hot, just very warm, the kind that won't burn) when she squirts.

For RD:

Rainbows when she's wet (possibly why her tail is rainbow-colored, hmm? It's naturally white, as opposed to her mane, but she's always horny, so...)
The "Filly Flash" was actually RD bringing herself to orgasm. That's right. Lightning.
Ordinary rain water when she squirts