… for Apple Final Cut Pro X
Tip #131: YouTube Share Settings Use Wrong Colors
4K files default to the wrong color space.
As you can see in this screen shot, the project settings are 4K frame size using Rec. 709 color space. (The settings are displayed at the very top.)
But the Share to YouTube settings default to Rec. 609, with no ability to change them back to Rec. 709.
NOTE: While the color values used in Rec. 601 (used for standard-def video) are similar to those in Rec. 709 (used for high-def video), they are not the same. Worse, FCP X should allow changing from one to the other, except that it doesn’t.
The workaround is to export your project as a master file (File > Share > Master File), then compress it using Compressor; or the compression program of your choice.