Some shield looks awful once you use any paint, since the metal parts won't be visible anymore.
For example:
https://i.redd.it/b1fr72rolvk51.jpg
Made a list of shields where I noticed this problem. there might be a lot more
Conqueror:
Lion's Den
Duellicosa (middle part)
Gladiator:
Pretty much every shield
Black Prior:
Revolt
Warlord:
Fafnir's Obsidian
Ebon Volkoff
Leos
Valkyrie:
Avaricious Wolves
Pyre