To make it easier at a glance to see what you've been working on I would like sub-tag colours to relate to the parent tag. do do this I usually manually pick a colour in the same part of the spectrum as the parent tag, but I think it would work just as well to 50% 50% mix a new random colour with the parent colour.

This could be the method of generating the default colour when you 'skip' a parent tag colour, then you can over-ride it as per usual.

Perhaps the percentage should be 70-30 or something else, but just so it looks related to the parent but not identical.