Here’s my solution (it’s the one in the book):
And here’s the link:
http://www.lodev.org/jstumble/?board=rrereree0ereerrelee0lreelrelererleelexeerelreerleli
Description: If you trace the left-most path, the only way a blue ball can get into the interceptor is if both of the bits are pointed right to start. Otherwise you end up with a red ball.