Gilded creates a metallic sheen on a limited area of the dragon’s body. Gilded will affect one color on the dragon other than the base color. Alternatively, it will affect a single trait (which might have multiple colors).
If you need advice making something look metallic, here are a few tutorials you can use:
The gilded marking still follows its normal rules. It only causes the trait to gain a metallic sheen.
Modifier, Claw, Leather, and Crest Rules
This only affects one marking on the dragon.
You may have up to three markings affected by gilded.