My two cents after looking at the photo......
The spot will eventually merge into his fur and everything on his body will get darker (spot will blend). Not sure if you can see Miko's tail in my avatar, it wasn't as dark as Justice's but it was pretty black too. Also, his fur was like your Miko's, tipped black. It just means he'll probably turn into a darker sable versus a lighter one. Check out my photos of Miko now. He's very dark. But he wasn't like that in the beginning.
Miko's black tail and black tipped fur (he was about 11 weeks here)
Miko as of Sunday
Do you know what Miko's parents look like? are they darker? I'm thinking the spot will blend as he matures and gets darker.

But until then, it's cute!
I'm still shocked at how light Miko was to how dark he is today. It took a long time for him to get that way. It was so subtle I didn't even realize it. lol