The game's brightness when playing through CEMU is completely blown out of proportions in comparison to the original on the Wii U. There is a graphics pack fix for this, so long as you have the latest graphics packs installed it's the last entry out of the Xenoblade graphics packs. Open Cemu and right click the game>edit graphics packs>(expand)Workarounds>(toggle on)Brightness>(set it to) WiiU Default - Brightness fix only Done.