This is an interesting one.
I have 8 Mega Bar 50's, bought in 2 batches of 4 each, several months apart.
I noticed this issue because I had to aim the lights at a white surface, and unfortunately, I couldn't quite use them as footlights or uplights. I probably should have just left them off. But at any rate:
The older set, when at RGB values at 100% and dimmer 100%, sure appear "white". The other 4 appear more purple-ish. It's noticable because I numbered the lights. First batch is 1-4, because they were the first 4. The second are 5-8. When I lay them out, they go 1 and 5, 2 and 6, 3 and 7, 4 and 8 as pairs and addressed like the lower number(this will be resolved on my current lighting design).
Any thoughts as to why they'd be inconsistent? They are consistent within the batches.
Regardless of the answer, I'm contacting sales in a few days to order some replacement parts I need anyways. The end caps on these things break too easy, and I need to order some of the knobs as well. Always good to have a small inventory of these field-replacable parts.