I got a storm potion via random event. However, I don't seem to like any of the pets available in the storm color except for the Noktoa and Kanis. Should I get the storm pet that I like or sell the potion?

All depends on what you like. Usually by the time Vesnali is over they release a bunch of pets in both Glade and Storm colors as this is the event both colors came to be. So if you don't know which pet you want you could hold onto the potion until the 4th. (Usually when they release new pets in new colors the potion prices rise as well.) But it's really your call.

You could change your pet into a Noktoa or Kanis and then use the potion. Also, in the future there may be other storm pets in the making. Of course, selling is fine, but besides that one time when the storm potion was in the token shop, and the random event, I don't think there are many chances to get another storm potion (unless you buy it from a user shop), so I would hang on to it.

But really it is up to you ^^