A little Mystery - what could it be?

I´ve got here a little mouse which has started to changing color. She is now about 8-9 weeks old. I Ask the Breeder I got the Buck from, she had similar happenings in the same line twice, and all are females, and changed when they where about 9 weeks old. I´m just wondering what this could be geneticly?

Father ist Geneticly: a[t]a[t] Bb dd Lghlgh Pp Sasa ss Vsvs
Mother, as far I know: a[t]- Cc Dd Frfr Lghlgh

The entired Litter had no spottings, and I never had spotted babies with the mother and an other Buck, so this is why it is so a mystery to me.

She started getting some spottings, neither she had no lighter pigmention in those areas as Baby, nor did she have it 4 Weeks ago. (See photos below).

So, did anyone here, breeding spotted Mice ever had something like this?

Here some Photos from now...








And this was wenn she was younger, sorry for the poor quality...



I had two Blue Tans in this Litter, but the other one, did and does not have anything like this!

Because these "Spots" are not pure white, more like a mix between White an the ground colouration (top Blue, belly Tan), it reminds me a lot of Roan. But I thought Roan only exists in the US?

Greetings,
Natasha