Is Melanin a PCR Inhibitor?
Melanin is a potent inhibitor of PCR - when you use B16 cells (or any other cell line that produces melanin) you have to purify your sample from it. Unfortunately a simple Phenol-Chloroform extraction or an ethanol precipation won't do the magic, since melanin co-precipitates with the nucleic acids.

I recommend following the following paper: "CTAB–Urea Method Purifies RNA from Melanin for cDNA Microarray Analysis".

The protocol derived from the paper can also be found here.