display wereas there is a tag for footway=*

FACT : It's quite difficult to see if there is already a tag to improve quality of mapping when a way has only highway=footway and not footway=* and perticularly footway=*.

SOLUTION : get more colours to let see when there are tags for each footway=sidewalk, crossing, access_aisle,traffic_island
In case of only highway=footway the colour purrple could let see that it needs the tag footway=*.

Start by locating the map rendering and colour-selection logic for highway=footway, then inspect how existing footway=* tags are represented. Done means the specified footway values have distinct colours and an unqualified highway=footway is visibly marked as needing a footway=* tag.

Written by the indexing model from the issue text.