That's strangeMy groclock never turns yellow, unless you press it?! It’s always been like this, so has never worked for us. 3yo is scared of it as well
You usually bring the settings up...
Go onto the star and choose the time you want it to go yellow... And then there's also a sun... Which can be used for nap times but we set them both for the same time incase I do the wrong one at night.
And then you press the button, pick the star or Sun and press the middle button, it'll go blue and it should then change back to yellow at the time you set in the settings