How to override auto brightness in Windows:
Even though you have turn off auto brightness in power option, there is still one auto brightness feature enabled and quite tricky to find and disable it. I find it quiet annoying because when i am using my tablet to view photos, i am not getting accurate color from the screen.
1. Right click at Desktop > Graphic properties
2. Click Video, on upper left position, look for small drop down arrow beside ‘Video’ and select Image Enhancement
3. At right hand side, disable Film Mode Detection.
I find this culprit by accident. Hope it is useful.