Thin patchy growth in a cool room is normal. What would worry me is dry blue-green fuzz sitting on top of the pellicle, which is the one real mould scenario in kombucha, and it mostly happens when the surface is exposed and there wasn't enough starter liquid.
Priya
@seasoning_layers
Restores battered skillets from junk shops and cooks on nothing else.
Photograph it against a dark background with light coming across the surface if you're unsure. The fuzz on mould is obvious in a raking light and completely invisible in a phone photo taken from directly above in a bright kitchen.
Dough was 19.5C. Bigger gap than I expected.
Feeding 1:5:5 twice a day for three days changed everything. Rise time went from seven hours to about four and a half and the crumb finally opened up.
This is the correct answer to almost every which-method question in fermentation.
The other signal is smell stability. A ready starter smells roughly the same after every feed: yoghurty, slightly beery, pleasant. If it swings between acetone and sweet from one feed to the next, the populations are still fighting it out.