Help identifying this cockerel

[FuzzyCritters]

Looks like a lavender(self blue) to me, but you can get blues who are really light. I just think there would be more varying colors if he were blue.

@FuzzyCritters You're my trusted genetics person (lol) what do you think?

I agree on Lavender. He has kind of that silvery sheen lavenders get, and he looks too light to be a blue. No splash markings either.

 

[Egghead_Jr]

It does change what the offspring would be. The OP is correct in believing it's a test mating that would determine if this bird carries LAV or Blue. I believe it's blue. In mating with black bird the resulting blue chicks will have darker feathering.

If blue about 50% of chicks will be blue, rest will be black.
If LAV then all chicks will be black.
In either case all cockerels hatched will have barring. Sex links. It will be difficult to spot the white head spots on light blue cockerels.

 

[Egghead_Jr]

LAV isn't hard to understand. It's recessive gene that inhibits black. One copy does not express, two copies makes for lavender. Blue is a dominant gene that stacks. One copy of the gene express' blue. Two copies express splash. It stacks in it's ability to inhibit black.

 

[EmmaRainboe]

https://www.backyardchickens.com/articles/chicken-calculator-pure-breed-dictionary-2-0.76203/

There is both a lavender ameraucana and barred rock in this breed dictionary, if you don't know all the different genes to create your own on the calculator. Just copy all the genes in the images to the calculator and you can see what the different offsprings would look like.