1. Making the sign for "color" (touch your chin with your index finger and then move it out and slightly up)
2. Then make the sign for "hair" (sign for "hair" is similar to the sign for "color" but you bring your index finger slightly upwards to your temple)
The sign for "gray" is made by combining the "color" and "hair" signs together. This combination of signs is often used to indicate other shades of hair color as well, such as "black hair" or "brown hair".
Let me know if you'd like to learn other colors in ASL!