Workout app has number in yellow.

Just before you start your next workout do this;

On the workout type tap on the 3 dots top right corner and then tap on Open then start a workout and when you've finished tap on end,the watch will remember your last setting and next time you do a workout it will be set to open goal.

I have this question too. For me my "Core Training' workout suddenly has a yellow 15 min goal (instead of a green 'Open Goal') that I didn't program, and I can't figure out how to get it back to an open goal. The 3 dots in the small circle don't offer any help in changing this. And added to that, my music stops during the workout to alert me that I'm at the halfway point and when I've hit 15 minutes which is even more annoying as music never stopped when I received any progress alerts prior to the OS 7 update.

This worked like a charm, my Core Training is back to Open Goal - thanks so much for the tip!

Yellow means you have set a time goal for the workout