[Chimera-users] drawing circles

Friends, I want to draw concentric circles of increasing sizes around the protein. To achieve this, i used the 'define plane' option to draw disk choosing I three reference atoms and drew the disks of increasing sizes and choose two different color for the inner and outer disk. Since the reference atoms are the same. If i change the color of the bigger disk, i get a weird appearance of the inner disk. I dnt know how to resolve this problem. I would like to know if i can do something like making the disk transparent/removing the fill color of the disk. thanks, Bala -- C. Balasubramanian