Short answer: stop your server, run rails assets:clobber, and restart your server.

I guess the question I have to ask: why did you run bin/rails assets:precompile? What that does is to create a static snapshot of your tailwind classes and put the results into your public/assets directory. If that directory exists when the server is started, puma will serve those files and never forward the request to rails at all. The end result is any tailwind classes you try to make use of will be ignored unless they are in that static snapshot.

What I did to reproduce the problem:

rails new play --css tailwind cd play rails generate scaffold say hello bin/dev 

Adding bg-green-600 to app/views/say/hello.html.erb worked at this point.

Stopping the server, running rails assets:precompile, restarting the server, and then changing the color to bg-sky-600 did not work - the background was white – this matched what you reported.

Stopping the server, running rails assets:clobber, and restarting the server, and I can see the new color. I can then change the color to bg-red-600 and see the results of my change.