Oh, thank you for the enlightenment! I've never had a chipmunk chick, so that is very helpful to know that what I get is "grey"...Dark and light hens look alike except Dark hens have grey and dark grey stripes in the down on the underside of their body and their bottom, while the Light hens are light brown in this area. Adult roos will have mainly white feathering, though patterned, but the Dark roos will have some darker coloring on their backs. In Light Jærhøns chicks the males are yellow, females are yellow with a visible brown stripe from their head and down along the back (chipmunk chicks). In the Dark Jærhøns chicks the males are light brown with a large uneven yellow spot in the head/neck area. Females are dark brown with a small spot on the head.
I think the hens you are calling light are what the Norwegians are call greys. The greys are not in their SOP, but some breeders in Norway are working on them. I think the E locus for Dark is eb, Light is e+ and both are gold ss. The Greys seem to be eb and may be genetically silver SS. I think some Darks are Ss(golden) as the hens neck color is slighter lighter in some Darks and this would be where the silver S comes from. The genetics are just theories on my part based on by observations and they may not be right. I am looking forward to learning more.