add colour field type

[k-yle]

Closes #26

Follow-up from openstreetmap/iD#8782 (comment)

This means we can more reliably detect colour fields (e.g. building:colour=*, roof:colour=*), rather than the current logic in iD which would erroneoulsy match tags like seamark:buoy_cardinal:colour_pattern=*

[tyrasd]

Thanks!

Could you please also add the new field type to the documentation on the readme?

done

[tyrasd]

Ah, one more thing. I overlooked that you chose the British spelling colour while one other field (localized) uses American spelling. I think it would probably be better if we remain consistent in that regard, wouldn't it?

//edit: Ah, wait. localized is also fine in British English. I must have remembered that one the wrong way around. Let's keep the spelling as is then. FWIW, the colour field in the presets repo also uses the BE spelling in the file name: https://github.com/openstreetmap/id-tagging-schema/blob/main/data/fields/colour.json

[1ec5]

@tyrasd, this PR is approved, but only you are able to merge. Is there anything holding up a merge, such as needing to migrate id-tagging-schema’s roof:colour field back to the colour field type?