Explain how material-ui uses a color palette

[Floriferous]

For each color palette (primary, accent, error, etc.), we have to either use default material design hues or provide our own. This requires a set of 15 hues. It is not clear to me (and so far haven't been able to find it here or in the docs, or on material.io) which hue is used in which context.

For example, why is A400 used here ?

It would be helpful to understand why and where hues are used, to make customization easier.

• I have searched the issues of this repository and believe that this is not a duplicate.

Tech	Version
Material-UI	next

[oliviertassinari]

@Floriferous The why is around following what the specification is asking for. I'm not sure we could provide a better explanation. We plan an simplifying the whole system with #8075.