I'm really glad to see this topic, it's something I've been reflecting a lot on.
The black roots are unfortunately fake, it's a trick used by many celebrities to make believe they don't have grey hair, everyone does it.
For Madonna it's so obvious, if you look at some pictures in the RHT she switches from small roots to exaggerated ones.
Unfortunately she hasn't had a good hairdresser for years, I really think Andy Lecompte isn't doing any good to her. Those huge black roots for instance are ugly. I miss Garren or Luigi Murenu... they did amazing stuff.
The blond color is something she's probably going to keep as it highlights the face and makes wrinkles less visible. But I would definitely be very happy if she'd try something new.
And I don't think she's ready for grey either. She does a lot of talk about anti-aging, but she's the first one to use fillers, dying her roots, etc... not very coherent even though I really think she look amazing, and most importantly, unlike many others, she DOES look like MADONNA, not like a kind of monster.
Go comment her Instagram pix, I'm sure she reads a lot of them, and maybe she'll decide to try something really new.