OK, I feel dumb.... I don't know what "an extended black chick at hatching" looks like. What does this mean?
The chick down color on a lavender should look exactly like an extended black chick at hatching. The lavender gene dilutes black and red, so the black portion of the chick would be lavender and the white or cream color areas will stay the same.
Down color is very important to look at when hatching birds of project varieties. Down color indicates what color you are working with and if it is not correct the bird is not correct in carrying the genes you want. It is a good tool to use to cull early.