How to gradually change the material of a ring?

I am currently making a rhythm game that requires players to click a button as their character is going through a ring. I want to indicate to the user how much time is left to get through a particular ring by changing the ring's texture.

I want the ring to start out as one solid color, then to have the other color slowly fill up the ring, similar to a pie chart would on a circle. If the new color fills up the ring entirely, the ring will disappear. However, I am very new to the materials/textures aspect of Unity, and I have no clue how to start making somet$$anonymous$$ng like t$$anonymous$$s. Is it even possible?

Thank you!