Spot on Bernie.
I have a Izumiya Yamabuki Ogon. I bought it as Nisai, and it was so light colored it looked like a low quality platinum. Later on this turns into the most beautifull yellow. Choose a bright yellow Tosai Yamabuki, and chances are they will turn orange or have orange spots!
When choosing Ogon, body is especially important since this is what you focus on since there is no pattern. Ogon have a tendency to have small pectoral fins, so when choosing a Tosai, look for pecs that seem way to big for the koi. Choose one with a good body, especially Ozutsu. Choose a light, evenly colored Yamabuki. And make sure all scales are in line and none of them are greyish in the centre.
Here's a link to a picture of my Yamabuki
http://www.nishikigoi-online.com/php...hp?pic_id=8076
Regenmeneer