One pastel colour per event_type returned by the find_*() functions,
chosen together with the soft blue and red plot_transcripts() uses for
the up- and down-regulated transcripts, so the eleven stay as far apart as
pastels allow, including under protanopia and deuteranopia. Pastels leave
less room between colours than saturated ones, which is why event exons
are also outlined and labelled with their type.