Nemeth rules about basic shapes are in Rule 17.1.
The circle shape symbol in Nemeth is 1246, 14 which is illustrated in Example 17-2. (1246 is the shape indicator and 14 is the letter c for circle)
When a shape is filled in or shaded, an indicator is placed right after the (1246) shape symbol:
The filled-in indicator is 456
The shaded indicator is 46
A filled-in ellipse and a shaded ellipse are illustrated in Examples 17-9 and 17-10. For a circle, the letter c (14) will be used instead of the letter e (15) for ellipse.
Whether a shape is shaded or filled in is a judgment call on your part. The two indicators allow for three different representations of a shape. In other words, "filled in" could be a color, "shaded" could be polka dots. If you feel your reader needs to know what the different circles look like in print, a transcriber's note can explain.