I did answer a question very similar to this a couple of days ago.
Magento 2 Development Process
This seems crazy in order just to see a font change colour!
Surely I must be missing something??
Is there a quick way to make css changes?!
I totally agree! There is a much better way.
Use a task runner like gulp or grunt to auto recompile and clear cache for you.
1) On your local environment disable Magento Cache. You really don't need to have this, but if you really want to keep it enabled you can also clear cache command line way with Grunt or Gulp.
2) Use Grunt or GULP (Grunt easier setup for me) to compile your LESS styles for the shortest feedback loop. Then you will not need to use sudo bin/magento setup:static-content:deploy en_US or en_GB every time. (Setup about 45 minutes - 1 hour if new to LESS I think -> less time if experienced)
Step 3 is optional and was not asked for in OP question but is helpful.
3) You could setup "Live Reload plugin" if you really want it to load automatically. It can detect change on your local files (which were just recompiled for you by your task runner because you saved your .LESS file) and reload in browser for you.
P.S. You will still need to run the setup:static-content:deploy command on production servers and environments.