Is this a bacterial colony?
These look like crystallization structures when liquids dry up. But if it were to be a living thing, I'd go with fungal colonies. In my opinion, the best methods to tell is to scrape off a small piece, flood with KOH, and observe under a microscope, if you see filaments then it is definitely a fungus, and alternatively you can inoculate an agar (Sabouraud agar could work, or LB agar) to see if something grows. If its a fungus, it can take from 4 days up to 3 weeks to grow depending on the species and the growth conditions provided.

Good luck.

Here's a ref that might help you.

Microscopic potassium hydroxide preparation: 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3994805/