Hi! Welcome to the forums!
Ok, just so I’m straight on this, you want a circle that changes color via a value, right?
If so, then this example window may be of help. This actually has two circles. One uses styles to change color from green to yellow to red to flashing red, the other uses a gradual change from green to yellow to red. I wrote this up to show my guys here that there are different ways to do the same task. Me, I like to make things visually pop. A little more effort up front, but usually worth the end result.
Also, to help you get familiar with what I did, please read up on the following in the manual:
Hope this helps!
EDIT: Removed non-existant file link. Reattached below.