I can't find anything about this problem I'm having in any search engine. I have a multicam clip and I'm trying to match the color of the 2 clips but I can not get the "Apply Match" button to work. It's grayed out.
I just ran into this issue today and found a solution that I wanted to share that worked for me. In my situation, working on re-editing a short film for someone, I was presented with a timeline that had a few off-line audio files. The files were temp tracks of music, so I left them offline in the timeline. However, I noticed if the off-line audio was connected to the video clip that you were attempting to match to, the "apply match" button is grayed out. Vice versa if you are attempting to match the color of a clip which happens to have an offline file connected to it to another clip in the timeline, command option M (the keyboard shortcut for matching) as well as Match Color from the magic wand "Enhancements" menu are not available.
In short, if matching color isn't available, make sure that you don't have any offline files connected to either clip in the equation. This may not have applied to your question but it fixed the problem for me.