Go here:
https://www.ennetran.com/Download
Drag the folders where your movies are located then select all the movies then select the profile "Strip Colour Header", then click Execute Profile. This is very fast.
If you want to make sure you have compatible audio so you can direct play, you can select the Add Dolby Digital 5.1 and Stereo profile. This will add streams to your existing mkv.
Well, I'm out. I ended up buying an Apple TV to solve the problem. Been a Roku user for 5+ years but not willing to edit thousands of files to fix the color/contrast distortion.
