The Galaxy S21 Ultra is expected to launch in just 2 colors, as its predecessor did before it. However, the latest leaks suggest that Samsung will add further options throughout the year. Meanwhile, other new tips purport to provide more evidence that it will be compatible with a new S Pen in 2021.
https://www.notebookcheck.net/The-latest-Samsung-Galaxy-S21-Ultra-renders-show-the-phone-with-the-S-Pen-and-in-new-post-launch-colors.509529.0.html