[Tag] Support colored tags

[conor-cafferkey-sociomantic]

Wanted

Add a color prop to Tag that accepts a CSS color value sets the background color to that value (and the text color to that value + a certain % darkness / lightness).

[uladzimir-dzmitrachkou-dunnhumby]

It might be better and easier to pass both the color and the background color as props, because otherwise it's tricky to get good contrast sometimes.