That's actually the Colour Swatch lua script, that he likely customized a little to get that palette.
You can get that script with the Reapack extension, which you can grab here :
http:///www.reapack.com . THis is the best option because when there's an update for the script, it'll get automatically updated when you synchronize(a Reapack thing).
Once all the scripts from the default repository are downloaded, you'll find it in the action list.
The toolbar icon may be his own design, but there are several in the Reaper stash at
https://stash.reaper.fm/browse.php?q=swatch&x=0&y=0
You can also make your own.