The move sequences given by Gerd in his comment are B d1–4; B 4–b5 and B d1–5; B 5–g6.
So, I gather that the following are all legal moves:
B d1-4
B 4-d1
B e8-5
B 5-e8
I think I misread an earlier answer. This actually describes one move on black spaces and the other move on white spaces:
If the bishop is on 4, then his path goes via b5, c6, d7 to e8. In the other direction it goes via b3, c2 to d1.
So, it looks like the diagonal from 4 to the first rank is a different color than 4, and the diagonal that goes from 5 to the last rank is a different color than 5, and that is how the color changing is done.
So, I gather that the following are all legal moves:
I think I misread an earlier answer. This actually describes one move on black spaces and the other move on white spaces:
So, it looks like the diagonal from 4 to the first rank is a different color than 4, and the diagonal that goes from 5 to the last rank is a different color than 5, and that is how the color changing is done.