I thought it would be useful to show the different types of effects that can be achieved through hand-dyeing.

Short Runs

For short runs of colour, the yarn is dyed in short lengths of multiple colours so that you get to change colour every few stitches and the colours are less likely to pool in one place.
Random Length

Random length variation occurs when the yarn is dyed literally at random. Some lengths of colour will be longer than others and the overall effect is a subtle blending of the colours, when colours of a similar hue are used.

If you prefer a subtle changes in shades of the same colour, semi-solid dyeing offers delicate transitions with no colour jars.
Medium Lengths

The effect of medium lengths of colour depends on the number of stitches you have selected for your project. With a small number of stitches, as shown in the example, you get an almost stripey effect. With socks, medium lengths can sometimes spiral round in pools of colour.