Hello.
This edit has multiple problems which should be corrected.
Unless an artist's name is literally "Unknown", if you don't know artist's name, it's perfectly fine to simply leave that tag empty.
Similar with the artwork name tag, if you don't know what it's called, leave it blank rather than writing "Unknown".

Additionally, in OSM all tags are ALWAYS in the lower case. Similarly, tag values, other than proper names, are also always in the lower case.
"color" is an invalid tag name. OSM uses the British English spelling of "colour" as documented on https://wiki.openstreetmap.org/wiki/Key:colour
"Greyish, blue" is invalid tag value for 2 reasons: in OSM if you list more than 1 value, they must be separated only by ; and "greyish" is not a valid name. https://wiki.openstreetmap.org/wiki/Key:colour#Colour_names lists valid names or use CSS hex code.

These issues should be correct.
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            Published using OSMCha: https://osmcha.org/changesets/165298368
            