COLORS: The American Sign Language (ASL) sign for "colors"
 

WHITE / BLACK / RED / GREEN / BLUE / BROWN / YELLOW / GRAY / GOLD / PINK / ORANGE / PURPLE /
/ PASTEL / VIOLET / CRIMSON / TAN / EMERALD / KHAKI / BEIGE / TURQUOISE / BURGUNDY / INDIGO / AQUA / MAGENTA / TEAL / MAUVE / CHARTREUSE / GOLDENROD / AZURE / VERMILION

To do the sign for "color" hold your hand up in front of your neck and chin area then flutter the fingertips.

COLOR:

QUESTION: How do you indicate that a color is dark?

ANSWER:
The common way to indicate darkness of a color is to sign "dark" before doing the color sign.

You can sign a color sign in a more intense manner while using an intense facial expression.
Adding intensity to a color sign doesn't specifically mean "dark" but rather it means "very."
If you add intensity to the signing of a bright color such as "white" it can mean "bright white."
If you add intensity to a color sign like yellow or green it can mean "vibrant yellow" or "vibrant green."

Notes: 

Also see: "COLOR"