Today whilst streaming on the LaylaCodesIt channel she noticed that my screen had a sepia tint to it. She said she had been experiencing the same issue.
After our stream, we chatted for a while and tried to figure out why we were both broadcasting yellow tinted screens. After 10 minutes of comparing streaming software and HDMI capture cards, I took look at the projection settings from my mac and noticed a setting called True Tone. By switching this off the yellow tint disappeared.
True Tone, is supposed to look at the ambient light color and brightness and adjust the output to ensure you have a natural-looking display. In a streaming scenario, this makes no sense, you simply want to be providing a clean version of your screen as other people will be watching it in very different lighting situations to the one you are in.
So before you stream, make sure you switch True Tone off.