Installing the Colors Live beta
The Windows beta is distributed through the Discord game library. To access it, head to the Colors Live Discord server, at the top of the channel list you should see a tag called Colors Live (Switch), click there, then click the Add to library button in the panel to the right.
Once the app has been added, go to your library by clicking the In Library header on the same panel. You should be able to install and launch the app from there!
To install an update, go to your Discord library and select the Colors Live beta. You may need to manually start the update install process by clicking the play button towards the top-right of the library page. One it has downloaded, you will be able to launch the app as normal.