After only having him for a little over 2 weeks, Draco (a crowntail) started showing what looked like the start of fungus or something abnormal growing out between the base of 2 of his rays. I worried and researched until I was blue in the face. I just decided to watch even more closely so I was sure of what it was before I treated. Turns out, he was just growing another ray (kinda goes sideways compared to the others though), and it never turned to the bright, vibrant red like the rest. Been several months now, still totally clear, and no signs of infection or injury, but still only half as long as the others.
Long story short, be cautious and careful to be sure there isn't an underlying problem, but hopefully it's harmless just like Draco's has been