Colin Has used artistic license with the colours on this picture and has pulled of a good result. The only area that could have been improved is the very light hairs over the top of the head and the ears; they stand out too much.
I would suggest that Colin carefully uses an ivory colour shaper to quieten these down this would have the effect of blending the light hairs into the mid tone colours.
I would use a light grey, say 270, rubbed into the whole background then add touches of 187 and 283 into this base colour here and there to add interest. I would use a slightly stronger application around the edge of the tongue.
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