Will these gray chicks keep their color? BA roo Partridge Rock hens.

[la dee da]

If the parents had that much white and yellow as chicks, then it must just be a fluke. It's normal for black chicks to have yellow or white bellies and chins, it's just not that common for it to extend up to the top of their heads.
I don't think it has anything to do the the lavender, they just looked suspiciously like mottled chicks with the white and yellow heads so I'd though you might also want to pay attention to those. Mottling would be another gene that would hide in the parents since it's recessive, but again, if the parents showed the same coloration then I would say it's just individual variation.

One of last year’s roosters did develop some mottling on his chest that was slowly molting out. I culled him for that.

 

[nuthatched]

I bought them from Sandhill, so I'm quite certain they're at least Australorps. They also look different from the (admittedly hatchery) Buff Orpingtons I had last year. That said, I can't be sure. It's exciting to think that they should keep the color!

I wanted to keep back an Australorp rooster to replace the jerk I have now, but I'm not so sure anymore. Could I stand having a black rooster over a lavender one if one of these chicks is a roo ?

I suppose chickens are like cats: the moment you think they're predictable, they throw you a curveball .

Sandhill likely won't know, their office and pen organization is terrible.

 

[Frizzle and Friends]

One of last year’s roosters did develop some mottling on his chest that was slowly molting out. I culled him for that.

Interesting. I know some birds that carry mottling may show some small mottles in their chest, wings, or around their face but I don't know how common it is. I'm still not certain the chicks have it, but it should be fairly obvious once they feather out. Mottled chicks will have black and white tuxedo juvenile feathers while black chicks will be solid black, maybe with some white wingtips. Substitute lavender for the black in the lavender chicks.
Though, mottling is another gene that should not be in Australorps, so I still don't know what is going on here. I will say it will be very interesting to see how these chicks grow out over time. They'll hopefully answer some of our questions about them and what is going on.

 

[la dee da]

Sandhill likely won't know, their office and pen organization is terrible.

I certainly hope they can figure it out. I’d like to know if I have mixed Australorps or a very unusual strain. I really want to cull my aggressive rooster, but if he’s too unique, would it be right to eat him?

 

[la dee da]

Interesting. I know some birds that carry mottling may show some small mottles in their chest, wings, or around their face but I don't know how common it is. I'm still not certain the chicks have it, but it should be fairly obvious once they feather out. Mottled chicks will have black and white tuxedo juvenile feathers while black chicks will be solid black, maybe with some white wingtips. Substitute lavender for the black in the lavender chicks.
Though, mottling is another gene that should not be in Australorps, so I still don't know what is going on here. I will say it will be very interesting to see how these chicks grow out over time. They'll hopefully answer some of our questions about them and what is going on.

I’m getting more and more excited to see how they turn out, though I may not keep them past week 6 or 8 (I have family waiting on pullets), depending on outdoor temperatures.

The best thing I can think of is some chicken (or chickens) got into the Australorp pen a generation ago, and I got chicks from that unknown mating.

 

[nuthatched]

I certainly hope they can figure it out. I’d like to know if I have mixed Australorps or a very unusual strain. I really want to cull my aggressive rooster, but if he’s too unique, would it be right to eat him?

You likely have mutts or low quality versions of something you didn't order.
Chop, chill and cheese him.

 

[la dee da]

You likely have mutts or low quality versions of something you didn't order.
Chop, chill and cheese him.

I figure I have mutts, but it’s fun to pretend otherwise for a while .

I’m realistically hoping a lavender orpington had gotten into the australorp pen. They’re close enough in personality for the babies to be nice chickens.

 

[Frizzle and Friends]

I was doing some digging on Sandhill's website trying to figure out how both lavender and possibly mottling got into what was assumedly Australorps and I found something. If you look at their Mottled Orpingtons listing, they state that they will be "black and white or grayish." What they don't say is whether it's blue or lavender causing the coloring. I would have guessed it would be blue since it's dominant and easy to get in a line. In their image of those Orpingtons though, they have a gray one and I'm inclined to say it's lavender. While the image is not great, it appears that the hen is lacking the darker hackles seen in blues. If other's want to chime in, it would be appreciated. If that's the case, then both of the genes you may be seeing may have occurred when a Lavender Mottled Orpington got into the Australorp pen. The other option is a Lavender Orpington or Mottled Orpington got into the other's pen, and they sold you the chicks from that crossing as Australorps.
Either way, this is only if the chicks have mottling. If they do not, then we can assume that the mix involved a Lavender Orpington. I do 100% agree that the birds you have are likely mixes.

Also, if your rooster is aggressive cull him. You've already hatched out a bunch of offspring and it stands to reason that one of the offspring with the interesting genes he has will be a male. There's no point in keeping a rooster that is trying to harm you or stressing the hens, he's not doing his job and there are better out there.

 

[la dee da]

Thank you! I was feeling bad about culling him, but I’m feeling better about it now. Your theory on what they are is very interesting, and these chickens being mixed would explain why they grew and matured at such various rates. I had assumed it was because of Sandhill breeding for fast growth and maturity.

I can’t seem to ever get good purebred chickens when I try to, so I’ll just enjoy what I have and breed whatever. Hopefully a lavender chick is male and has a good temperament.