The purpose of this exercise is to develop more skill at blending colors.
Colors: White, Red, Black
Brushes: use a Filbert to block in. Then use a small Bright brush to tighten the outer edges.
Use you roll of masking tape as a template to draw your circle.
Draw the internal rings.
Paint them as shown of the left.
While still wet, blend the Value Zones to make the red sphere on the right.
Here is another example: