These LEDs have been in use for about 3.5 years now. 28 out of 64 show discolouration. Fortunately these are used as a source of indirect light, bouncing off of a slightly yellow-ish wall. The effect is noticeable, but not really annoying.
However, if these LEDs were used as initially planned (down-light for a working surface), it would be a major issue. These LEDs were acquired on ebay for not too much money. Maybe that is the root problem here.
As far as I can remember, I did make sure not to overdrive them. The emitters are connected 4-in-a-row. If variation in drive-current were the issue, I’d expect groups of 4 to change in the same way, but that is not the case. I blame variations in the LEDs themselves.