My problem sounds similar as I can duplicate it on white screens as well. I keep my brightness lower so I find it a bit easier to notice to be honest. I keep it under 33% - more like ~25% brightness. Here is a ticket I just entered with HTC Support. I'm interested if you guys feel like trying it out and if you get the same results. My ticket detail is below:
[Brian Binder | May 30, 2013 | 10:56 PM]
Hello - I have been doing some searching on the forums...and everywhere on the infamous screen flickering issues on the HTC One. I have never experienced this with a phone before...I came from a plain iPhone 4 and wanted to give this one a shot because I really really loved what it had to offer.
I am running into the same screen flickering issues that others are having. I have turned off all power management, disabled auto brightness, moved the brightness slider under 25%, over 75%, and so on and so forth. Also not using a screen protector that even comes close to the sensor.
It hasn't helped much at all. What I will tell you I have noticed, is that it seems to have something to do with the proximity sensor. If I cover it with my hand, I no longer experience the issues from my testing so far.
I have uploaded a screenshot - if it doesn't make it through, you can access it here:
Screenshot ?2013-05-27 17.23.28.jpg?
The picture is a photo that I took that illustrates the issue. To see what I am talking about, grab an HTC One and put this wallpaper in your gallery and view it in landscape mode to fill the screen.
Hold the HTC One directly in front of you, about a foot from your face in the normal fashion. Now start to face the phone up towards the ceiling instead of at your face (tilt it backwards 90 degrees). Once you start tilting the device and the proximity sensor detects this, you'll notice that the red colors in the flag begin to change colors. It's not an eye trick - it happens and I can maybe catch it on video. For me, it's been easy to reproduce. If I do it rather quickly, the change is noticeable - like an extended flicker that either lightens or darkens the screen - though because of the color contrasts on the red and white, you notice the change and it becomes more than just a subtle annoyance on white pages.
Now, if I do the same test, but cover the proximity sensor (which is completely clean) with my finger, I cannot reproduce the same results as when it is not covered.
Do you guys have any suggestions? I'm hoping that my findings might help you solve this issue in a software update. If there was a way to manually turn off the proximity sensor as a system setting, it would be a pretty clear answer on whether I'm on to something, but I don't think that's an option.
Thanks for any help,
Brian