Thanks for posting your query.
The cut would be due to frenulem tear.It is the part which connects glans
with the body.
It would occur in cases of more retraction of glans as in forceful masturbation
With rest for few days it would subside and you can take analgesics for pain.
Regarding whiteness if it is milky white, without any itching it would be Vitiligo
. Keep the part dry. Even wet part would look little white.
Try with above measures and if it does not subside I suggest you to consult a Dermatologist
Hope I have answered your query.
Wishing you good health.