GRAPHREP
SET x_param:1cm 
SET y_param:1cm

FILL color:blue
ELLIPSE x:c y:c rx:(x_param) ry:(y_param)

FILL color:white
ELLIPSE x:c y:c rx:(0.666*x_param) ry:(0.666*y_param)

FILL color:orange
ELLIPSE x:c y:c rx:(0.333*x_param) ry:(0.333*y_param)