Colour in with your computer. This post shows one method of digital colouring, but it can easily be adapted with other graphic programs or for those who like to paint in the traditional way - watercolours.
I am using an old version of Photoshop.
Choose your image, this one is public domain. Click to see a bigger image and save to your machine for practice and/or clipart.
Make a layer and choose your palette. I'm using these colours. Going to the trouble of doing this saves time - selecting them with the eye dropper tool - and keeps your image results consistent.
Fill the hat first. This was done with a normal brush, using 'Behind' mode. Essentially your are colouring from behind, so the outlines remain in tact.
Grab your blue, a blurred edged brush 'Behind' mode and reduce opacity, for shadows in the beard. Just go over where there are lots of lines together in the beard. You don't have to do it everywhere there are lines.
Grab your grey, small solid brush, 'Behind' mode and go around the hair edges and the tips of beard.
Grab the flesh colour, big blurred edge brush, reduced opacity and fill the face in.
Change to a smaller sized brush, go around the face edge, down the cheeks to where the beard starts, where the mouth is and over all the facial lines in the face to bring the features out.
Complete! Click to see larger image and 'right click' to save to your machine for clipart.