Maybe a partially laced gold-silver split?
"Partially laced" because I can't think of any other logical thing to call that pattern.
"Gold-silver split" meaning a chicken that has one copy of the gold gene and one copy of the silver gene. Chickens that have both the gold and silver genes show mostly silver (which is why it is considered dominant), but the silver can be yellowish (presumably affected by the recessive gold gene they are carrying.)
If he could be a from a project or a variety that is still being developed, that would explain why he does not look right for any specific one that you can find.