I’m not sure what you mean by “light buff”. Light buff is not a recognized Ameraucana color, buff is.
Splash is made with the blue feather gene, so what you have are not true splash. When you show chickens, the judge does not look at genetics though, just the chicken. If the colors are right the judge will accept the bird regardless of what genetics made the color. However, if you look at this Ameraucana Breeders Club page, you’ll see that Splash is not an accepted color. I don’t show chickens but I’d assume you could not show a splash Ameraucana since it is not an accepted color. I could be wrong, maybe it could be shown under “blue”. If I am wrong hopefully someone with direct knowledge will correct me.
http://ameraucanabreedersclub.org/standard.html
Buff can have some strange effects on black. In theory when you cross a black chicken with a buff chicken you get a solid black chicken, but reality often does not work that way. Buff has some strong modifiers in it that can and often does change some feathers from black to some other color, sometimes yellow, sometimes orange. The shade can vary a lot from different crosses. This can be a few scattered feathers, it can be some pretty big areas. I don’t know if you are looking at the down or the feathers of the chicks?
What you are describing just doesn’t sound right, the black areas should be pretty pronounced. How sure are you that they are both true Ameraucana? But chicken genetics can be pretty messy. I can actually come up with a scenario where you could get something pretty similar to what you describe, especially if you are talking feathers and not down. Just how white are those chicks? Dominant White only affects black feathers. A pure buff chicken would not show it. If your buff has dominant white, that would change what should be black chicks in the offspring to a yellow that would feather out white. It’s possible that some black could leak through, thus giving you a few scattered black feathers when crossed with a black chicken. I’s kind of farfetched but with chicken genetics about anything is possible.
