Gilded gold, painted lily

After publishing a poem with gilded lilies, I wanted to find out what exactly the expression means and from whence it came.

Apparently from Shakespeare, who wrote in King John:

SALISBURY:
Therefore, to be possess'd with double pomp,
To guard a title that was rich before,
To gild refined gold, to paint the lily,
To throw a perfume on the violet,
To smooth the ice, or add another hue
Unto the rainbow, or with taper-light
To seek the beauteous eye of heaven to garnish,
Is wasteful and ridiculous excess.

Which means that the expression is actually an incorrect quote. It is the gold that is gilded, while the lily gets painted, both actions denoting superfluous adornment.