Usually only red dragons will mate with other red dragons, etc. But if a mating took place between a gold and a green dragon, the result might be a bronze coloured hatchling. Scales on a dragon are never simply one shade of colour. If a dragon is blue, there will be many, many shades of blue. Light, medium, dark, blue-black, etc.
Scales are bright and shiny in a healthy dragon, but dull and bleak if a dragon is ill.
In some breeds, when the dragon is mature, the cells in the scales are able to change colour, such as a chameleon, due to chromatophore, the pigment cells in the scales. If the dragon is angered it can change from its original colour to a bright, fierce colour such as firey-red, to look more intimidating or during mating rituals, it can flow certain colour patterns on its body to attract other dragons. Since dragons are extremely intelligent, it can choose which colours to change into to match the exact background it is near including subtle shadow and highlights. It is so skilled at this, most things would just walk past a 65 foot dragon hiding in the sand. The main function of scales is protection of the soft skin tissue of the dragon.