Gray is the most neutral color you could possibly get. It's dull and monotonous if used improperly, but there are many ways to make it more interesting. For a general example, more appealing neutral grays are slightly bluish.
The gray is least interesting when you have all RGB channels set to the same value, so generally you'll want to tinge it with a bit of color. In fact, RGB grays are mostly useful as a great starting point. And you'll want to tweak the neutral grays from there until you're happy with the hue you've achieved.
General Rules
- Generally, avoid having all three RGB values identical to each other.
- You can start with a neutral RGB gray and tweak the RGB values to add some warmth or coolness to the gray.