Saya had yellow hair so is not saya Nu have white hair and that braid style of hair and an obssesion to be with ragna so is Nu not Lambda but in Blazblue CS Nu's mind is in Lambda body and sacrificed herself to protect ragna
I think that the entire family had Blonde hair and Ragna's turned white when Rachel bit him I'm going to assume that it's Saya since Ragna spent more time with her. I think it's just the colour scheme that the artist used