Because some people asked me, how to colour the drawings in photoshop, I thought it would be useful to make a tutorial for it here.
So, let's start.
(Sorry that the descriptions are german, but I think you can still find the options, because the positions should be the same.)
1st Step: Open folder

Well, this step shouldn't be one of the more difficult ones.
2nd Step: Colour some regions in pure white

This is needed to set the whole background in pure white. This way the colours will keep the same later when colouring. Obviously this works only, when the background is white. (Like paper)
3rd Step: Set brightness and contrast


Set the brightness so high, that the white coloured areas aren't visible anymore, BUT NOT HIGHER. Then set the contrast so high, that the drawing itself is clearly visible. Now the whole background is pure white and doesn't mess with the colours, while the drawing is just as visible as before.
4th Step: Convert background to layer

Photoshop automatically sets the original layer as "background". A background can't be moved in the layer hierarchy and thus will always be "in the background" behind all other layers. But we want it on the top in the very front of the picture, so we have to convert it into a layer.
5th Step: Set the layer's attribute to multiply

Right click on layer -> filling options -> filling method -> multiply. This way we can colour behind this layer, but the drawing lines are still visible.
6th Step: New layer

Layer -> new -> layer. On this layer we will colour the picture. Note, that the original layer should always remain at the top.
7th Step: Colour the layer


Now choose one part of the drawing (in this case: the body) and fill in the colour with the brush. Do NOT use the filling tool and don't start colouring the other parts of the picture.
8th Step: Repeat layering and colouring for each part of the picture

Make a new layer for each part of the picture. You can look in the layer list at the bottom, if you're unsure, which is considered as its own part. Splitting the colouring up in different layers will make shading and highlighting a lot easier.
9th Step: Add shadows

Now choose layer you want to shade and the burn tool. It is selected in the picture on the left hand tool bar. If there is not the hand, then rightclick on the button and choose the hand. Then add shadows to the picture. Think about where the light comes from. Also, if the area needs a special structure, then you can do it in this step. (Like it is done with the feathers.)
10th Step: Add highlights

Remain at the current layer and choose the dodge tool. (Same button -> rightclick -> lollipop-formed symbol) Use it similar as the burn tool, but highlight the areas, where the most light would be. This step is also useful to add structure to the picture.
11th Step: Shade and highlight the other layers

Repeat steps 9 and 10 for the other layers. Think about the structure for each layer.
12th Step: Add background

Now make a new layer behind all others. It will be the background. Draw a landscape or whatever appeals to you. Of course you can just skip this step.
13th Step: Add real shadow

Create a new layer right in front of the background and colour the area, where the shadow of the object should be, black. Then set its opacity so, that it doesn't look too dark but not too bright. (54% in this example)
14th Step: Look at your finished picture

This is by far the most difficult step, but with enough training and patience you will solve this as well.

Your drawing is coloured! Congratulations!