Possible Clues:

• Golden shamrock necklace on St. Patrick's Day, e.g.?
• Staining damage linked with expensive jewellery
• Feature of Porterhouse that's blemish on conspicuous wealth?
• Spoil jewellery, adding mottled effect
• Streaks of butter round black fish
• Mottled effect is blight on jewellery
• Damage on jewellery that gives a streaky appearance
• Streaky lines spoil ostentatious accessories
• Mottled effect
• Streaky lines spoil jewellery