Gild the lily
To gild the lily means to over-embellish or to improve on something needlessly. The concept if not the actual wording is from Shakespeare King John Act IV, Scene II,“To gild refined gold to paint the lily … is wasteful and ridiculous excess.” Shakespeare’s drift is easy to follow. To paint a lily with refined gold is senseless, because a lily is already perfectly beautiful in itself. Somewhere along the line, Shakespeare's wording was simply shortened to 'gild the lily', which first appears in this exact form during the 19th century.