Concentrate when your good enough, to really get the edges in certain areas, nice and crisp. It will add a bit of realism to the picture.
And its alot of greys. Colors of owls are never fully grey. If alot of stuff was grey, then it would be a black and white painting with a drop of color. They are just really variants of really dark colors. Mostly its dark brown or a dark blue. I think in a way its ok to start out grey, and you can count as an underpanting (via a value/greyscalepainting). Then overlay colors on top.
Yes, I know. My point still stands that colors in a picture are usually never just a pure black or even grey in a sense. It makes the picture look flat if your going for colors. The face of the owl, is a bluish tone of brown. I can also guess its a bit desaturated because this is taken during a cloudy day.
If your really getting close to the reference, it needs alot more contrast. Don't do the details first, block in the shapes generically (even values) then go back and do the detailing.