Generate a continuous sequence of distinct random colours for diagrams.
Sampling is done in the Lab color space so that perceptually different colours are generated for the given lightnesses.
Further work: Instead of taking flat slices of lightness, take all samples to be the same distance (in Lab-space) from a given point (i.e. the background color). This should give a more consistent and pleasing amount of contrast.
Update 2015-09-24: advanced version implemented (here).