it might be heat related but ~27C isn't so bad. It likely is more robust in a week that you don't see it anymore.
if you have been controlling pH of what water you use and not overfertilizing, etc.. all is well.
also difficult to see color under some lights, mine too. my leaves are much darker under normal lights, which i bet yours are too... if fan is directly hitting it, that may not be optimal. can string them up to ceiling and adjust height as needed, if not a clip on.