If animals are 66% het. for a recessive trait it means that 66% of the animals are het. and not that each animal is 66% het. If you breed two 100% het. Clowns together you will get: (in theory)
1/4 Clowns
1/2 100% het. Clowns
1/4 normals
So of all the normal looking animals (3/4 or 75%) 2/3 or 66% is 100% het. Clown (in theory). Only problem is that there´s no visual difference between the hets. and the normals so the animals will be sold as 66% possible het.
Hopefully this clears things up.
Regards,
Bas