Why didn't France wear a blue jersey and Italy did?

Because the French team is in the penultimate group, but also in the second place in the group, according to the pyramid distribution map of the knockout stage, the penultimate player will always wear the visiting team jersey during the knockout stage, so the French team will always wear white clothes from 1/8 to the final.

On the contrary, if the French team walks out of the line in the state of group 1, then they will wear blue, white, white and blue respectively in the four knockout matches.

This was not decided by drawing lots before the final.