Good Colormaps?

What are good colormaps for these colors?

Black?

Help is welcomed.

Black is #000000.
25% Gray is #404040
50% Gray is #808080
75% Gray is #C0C0C0

Basically any color in the grayscale will have the same value in all RGB components, for example, 25% Gray is 0x40 Red, 0x40 Green, 0x40 Blue (0x40 is the hexadecimal value for 64 in decimal base).

Thanks for the help.