Issue description

It would be nice to add support for querying the cursor color. As of Tmux 3.4, users can query the fg/bg colors using OSC10/OSC11, but not OSC12. The Xterm control sequences specs also uses OSC 12 ? to query the cursor color.

Here's a picture from Ghostty with the cursor color changed

Required information

Please provide the following information:

• tmux version (tmux -V). tmux 3.4
• Platform (uname -sp). Darwin arm
• $TERM inside and outside of tmux (echo $TERM). tmux-256color
• Logs from tmux (tmux kill-server; tmux -vv new). N\A