Also light and shadows falling on blond hair and days gone with out a wash (the oils settle on the hair to give it a darker appearance) can register a bit darker color in pictures. You can also often tell by skin color if the woman is a natural. Much of this is hard to decipher in pictures.
Elin is clearly a natural blond (although she may get highlights to enhance the lightness especially now after the children.)
My guess is that Kate Moss is a brunette.
I’ll say more but....take a better look at Elin. She definitely shows dark roots in some photos. Blond hair is made of thinner individual hairs but coloring it thickens it. Sometimes to point of the hair plating together and sticking together. Elin shows this too (from my looking at her)