Reddoss

This is my first post and am new to this forum so forgive me if this question has been asked before. I have had my HX for a few months now. About 4 weeks ago all the different colour coded LEDs (e.g. green for delay, blue for modulation etc) all started to turn yellow after about 30 mins or so, the sound is not effected at all. Is this a temperature thing. If I switch it off for a while, the normal colours return. What is happening, and how can I prevent it from happening?