It looks to me like it's that mock cathedral window pattern, made by sewing two circles of fabric together right sides together, then turning right sides out through a slit in the white fabric which is located towards the side and then covered up when the circles are sewn together forming 4 half circle "flaps". In this case the colored circle used initially is pieced of four quarter square triangles. Very pretty and interesting. I've never seen it done with that circle pieced like that.