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For me just toggling on colour filters without adjusting the sliders toned down the yellow of True Tone.
 
This does not work. At first I thought it does, but it was just trick on my eyes. True tone is same dark yellow with slider all the way left or even all the way to the right. Just try to turn off true tone again and after while turn it on, you will se the dark yellow back
 
True Tone seems to adjust the yellow color of my phone and nothing else. I hope this gets updated in a future iOS release, so blue and green are more involved.
 
Strange, I was getting yellow tint. Tried everything on this page including colour filters and either did not change or did not like the results. Then turned off colour filter and the previous yellow tint was gone. The screen now matches my iPad Pro True Tone :)
 
Not a fan of true tone. I prefer cooler whites. Which might explain why I bought cool white 6k LED interior lights for my car and any clear Christmas lights I buy are, again, cool white.

Good luck to whoever struggles with this dilemma. My 6+ looks a bit cooler next to an X, but once I get an X, the 6+ will be traded in or sold so I won't have anything to constantly compare.
 
I didn’t like the over warmth of True Tone on the iPhone X, but with. Little experimenting I found having a dark wallpaper generally reduces the hue. Your eyes aren’t shocked by the bright screen anymore and adjust to the ambience
 
WOW!

Idk if it’s just me or if this is actually real but I DO notice a difference. Amazing. Thanks man

EDIT:

After reading more posts it really might just be placebo effect.

I wish someone had before after pics or something.
 
I had your problem. I resolved with an hard reset of my yellowish iPhone XS.
Now under the same light it has the same white point of my iPad Pro with True Tone on.
 
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