https://www.apple.com/feedback/ipad.html
To modify screen colour temperatures during evening hours, I have been using the f.lux app on my Macs for years.
I was quite looking forward to using it on my iPad, particularly for reading, but it seems Apple has not provided the necessary documented APIs, nor is Apple allowing side loading of apps using Xcode 7. https://justgetflux.com/sideload/
This is why iPad will never replace the PC.
Hopefully you will open up the capabilities needed to make f.lux a first class app, or work with them to build the features into a future revision of iOS.