It's from them being silver instead of gold like their mothers.
Silver/gold is sex linked genes. The RIR have gold that's why they have gold tone (red).
Looks like your rooster carries one silver gene and one gold gene. With sex linked genes the daughter's don't get a gene from their mothers so...
I wouldn't hardly consider an EE a dual purpose bird and crossed with a Leghorn would be even less of one.
Depends on the egg color genes the EE carries and since that could be anything it's hard to say.