Sounds like your source may not be totally honest.  For one thing I suspect that you got melanotan II.  That would explain darkening of skin.  Do not misunderstand me; melanotan II will work just fine as a libido enhancer.  You probably need to inject.  I don't think other techniques work nearly as well.  
 
I've tried melanotan II for 5+ years.  It works!!!

melanotan II results in increasing libido much as bremelanotide (PT-141).  I think many suppliers actually sell melanotan II because it may be cheaper to produce and the only difference is that you can get tan.  I do not know your supplier.  
It "works" means that it gives you raging erections and horny horny horny.  I hope that is clear enough.  I pinch the fat on my stomach so it sticks out about an inch or more.  I inject into the pinched area with an auto-injector called "autoject 2".  The needle I'd recommend is a 31 gage 3/10cc model with a 5/16 needle.  I insert the entire needle since it is small.
 
Also: do not use more than 2mg or you will get a stomach ache.