Initially, i thought to so but I wanted to keep the color effect only because of the tones richness, which could help to give more life to the work. But, i'm sure the grey shades would be fine too. Thanks for the suggestion.
ya, each artist has also his own idea for sketches and desired final effect. Let's say that the colored ones can be just a little more rich for visual appealing and emotional thoughts; in the other way I see the b/w ones as for more dramatic and deep reactions, maybe they are more instinctive - we like it, or say definitely not!