Better colour fields

[nlehuby]

It would be great to have a special field to render the colour from the tags colour, roof:colour, building:colour, etc

Something like what github does for instance (when you type #CD853F, github turns it to #CD853F) or like this web component:

[nlehuby]

FYI, it has been done in osm.org:

[tyrasd]

for reference: this was mostly fixed in #8782