Possible to render a simple colored spot rather than use a PNG?

Hi all, hope you can offer some advice

If we were making a game like FLOW (Click here to see FLOW) and all we needed were some simple colored circles which the user must click and drag, then can these be rendered by Unity, or do we need to actually import a PNG of a circle?

I am sure Unity would be capable of rendering a flat solid circle, which I think would look better and behave better when scaling up/down? And would it be lighter/more efficient on the game engine?

Whats the best solution?

Thanks a lot