The below should get you started. You could use VectorToRadialValue to mask a texture, or a generated circle like I did below. The “Percent” is a scalar parameter node, it should go from 0 to 1, you can change that from a blueprint. The “color” is a vector parameter node.
The custom rotator can be adjusted to where you’d like the circle to start from (when at 0), the rotation angle goes from 0 - 1, so .25, is 90 degrees, and .75 is 270 degrees etc.
Set the ConstantBiasScale node to have -0.5 in Bias, and 1 in scale
