Hi well Kohaku is in the history of Ki goi and was first produced back in the 1930's by croissing with kohaku and Asagi (white type) so a Back cross in breeding terms and you do get flesh colour ones,white ones and red ones ,as well as yellow as its all in the background genes .
Akemi ki goi -red eyed type also turn up in Kohaku spawns now and then as its no wonder Akemi Ki goi are used to improve the line as its a more pure type when breeding so better results are seen .
As most Ki goi have better body shape and size and don't carry black like Magoi and so less culling also ,so easy breeeding when using this type of koi for breeding .
I also get them turn up in Shusui breeding as the Asagi gene is there ,and can produce some intresting koi ,like white Doitsu Akemi shiro goi and red akemi doitsu.