[elunned]

There is a difference. I have a thread saved off the NI board from April of 2004 in which JR posted a number of photos showing the difference between kohaku eyes and sanke eyes. (Unfortunately, nothing on that board is archived.) A typical sanke eye has a 'silver fern' pattern surrounding the pupil and a sky blue eye lid. Because high quality kohaku lack the ability to produce melanin, the eye tissue surrounding the pupil is plain and the eye lid clear white. A koi that might be correctly benched as a 'kohaku' could have sanke genes - and the eye appearance is a good indicator of what you might expect as the koi matures. Kohaku with sanke backgrounds are much more prone to develop shimmis.