It might be normal for you, but you should really get it checked out. Since it appeared out of nowhere 8 months ago, and assuming you're at least close to adulthood, so since it's new, you should get it checked out.
There is something called penile melanosis that may be causing this - https://www.healthline.com/health/penile-melanosis. It's totally harmless, but you should get it checked out to make sure it's this and not something else that needs treatment.
Let us know what happens.