It's experimenting on software, not experimenting on people. "People" aren't the part of the equation that anyone cares about in this scenario.
And I do not think you're even sort of having this argument in good faith. You can't possibly be a rational person and believe that changing UI colors is "deeply problematic experimentation on people".
Forgive me if I'm a little pissed off but this privacy extremism shit is exactly what leads to people looking down at anyone who is a privacy advocate as a nutjob. So, thanks a lot for that, more work for those of us out there who want, to, I dunno, protect citizens from being genuinely fucking spied on and their data passed around like candy so better ads can be served.
But hey, it's all good, you're keeping those pesky UI designers from knowing which of their redesign is better, so at least we got that going for us.