Yellow head and tail

[ybor_knight]

Anyone know what would cause a koi's head and tail to turn a yellowish tint?
The fish seem to be behaving normaly, very active. Just happen to have a strange yellow tint.

[Terri]

Has it always had this yellow tint? What variety is it? (kohaku/sanke/utsuri) How old? Got a photo?

Yellowing,
.... water quality - namely ammonia at low levels over a period of time - and/or mid to higher DOC levels (DOC-disolved organic carbon(compounds)),.... etc.
.... age of fish - shiroji (white) development stages
.... poor genetics

[Jackie Ramo]

In addition it could be cold water stress. With the temp swings at this time of year it is quite stressful.