Hey Larz
Indeed, a sharing from GCSpyder and the others should be great. Anyway, the following links might be useful for the Mystic/Bito shiro grow out participants. Hope Mr. Hwong and Welson don't mind.
This link contains recap by Mr. Hwong from seminar on Omosako Shiro by Takayoshi himself, this seminar was held during SPKC Omosako Shiro grow-out judging session.
Koi Forum (Nishikigoi - Japanese Koi Fish): KOI Talk: Koi Appreciation: My New Shiro Utsuri
And below I quote lessons learned from Welson (wtansk) taken from this link
Omosako Shiro Utsuri Grow Out Event 2006 - Page 9 - SPKC Koi Forum
"I had learned the following during the talk:
1. If two koi, one with white head and the other with yellow head, he will pick the one with yellow head to be a male. (hehe.. I always believe this)
2. Shiro with yellow head that turns to be a female will have more stable sumi.
3. Instead of putting your money on 1 koi, split the money to invest on on koi with different characteristic to see how the koi will grow in your water.
4. At young age, most important is the balance body and not the overall body confirmation.
5. For Omosako shiro, if sumi dot appear at several location, it will have sumi but need to be patient."
As for me, I learn a few hard lessons from both Omosako shiro grow-out events that I followed closely


. My two cents:
- a white head won't give you a guarantee, it can turn yellow later. the opposite is true
- a narrow looking head can still give you a nice head shape later, provided the fish looks underfed when you choose it
- a dirty head will guarantee a head sumi, but you can not tell what it will look like
- pattern will follow underlying sumi (here I mean sunken looking sumi, scallop looking sumi, net like sumi, NOT the peppery sumi -- other call it baby sumi --)
- I don't have to worry about shiro and sumi quality if it is an Omosako shiro

, but I need to worry about unwanted hi later if the fish is an offspring of Musashi

I'm not trying to say that all will develop unwanted hi, but the fact is some do. And even when they do, in some case the hi comes and goes. So it'll go back to your luck.