The letraset Promarkers are professional art markers for Artists and I used the Neutral tones which are shades of grey to color in this rather old drawing I did with an ink pen last year. The Promarkers are excellent for blending various tones of color together and can be layered upon each other to create vastly different and richer tones.
The ink drawing is of a Demons head (No surprise there!) and I was happy at the end result of this quick colored piece of art. You can also look at the video I did here - Promarker Neutral Tones Art