Feature Request: Add a way to manage groups of colors

[untemps]

Sometimes, it would be useful to split the slots of colors into groups, to create collections for instance. The colors prop could be set with an array of specific object, like so:

const colors = [
  { name: 'Yellows', colors: ['#ff0', '#0f0', '#0ff'] }
]

Expected issues:

• The compactColorIndices is not relevant for groups of colors: what indices of are they?
• It might be difficult to mix single colors and group of colors: a choice in the API has to be made, to restrict to one type of entry for example