Life, welcome to the forum bro....!!  The old shadow you are referring to will always be there and there is nothing you can do about it unless you go for laser treatments or it eventually falls out on it's own. However, as you age and if your hair turns gray or white it will be less noticable also....there are some guys here that have been through the laser treatments and they might have some more advice for you....Good luck to you and keep it sly   

Hey Brother,
There are a few things you can do but depending on your hairtype there might always be alittle bit of one. 

-Get a good razor,
I use a Mach 3 (and sometimes Headblade).  This can make a difference. 

-Do proper prep. 
Do something to soften up the hair and scalp.  Shaving after a shower is good to soften up the hair and get it closer.  I read somewhere that you're hair takes 2 mins of being soaked in shaving cream to fully soften up.  What I do is cream up my whole head (after a shower) and shave my face or brush my teeth while that head hair softens up. 

-Go against the grain. 
On the side hair against the grain will be straight up.  Don't cut yourself, but put some solid pressure against that blade. 

-Do a quality check. 
Rub your head.  If you feel ANY stubble AT ALL, Then you didn't do one of the above things correctly.  If you feel any stubble follow steps 1-3 of my shaving methods again.  Sometimes in the back you'll have to go over it again. 



If your head is as smooth as a baby's butt and there's still a shadow then there may be no way to truly get rid of it.  You could try getting alittle sun on your dome and that should help (but please don't burn it, there is a lot of info on the site about that).