Yes, the coloured ones take actually a lot longer than the ones with pencils (and even longer than the one with acrylics), because I have to draw every hair individually.
It took about a week to make sketches (which took one hour per day, including staring at the photo and at Ben's fur to get the colours right), and for the final drawing, I needed... let me think... three days, with about 4 hours each.
A pencil drawing takes less, because I don't have to worry about the different colours.
Pastells are much easier as well, because you can fill the space with it. With coloured pencils, when you have to draw ever single hair individually, it takes ages! If you want to mix colours, you don't overlay, you have to draw the lines side by side to get the effect.
I actually also drew the white hair (Patty), the photo does not show it, but it is not just the paper shining through, it is white pencil. On the original, you can see it properly.
It was ever harder with the drawing of Ben. He has so many different shades of brown, and the drawing is bigger than the "original Ben face" so I had to be very careful.