|Billy Lowe and color client - highlights only|
My answer to that is - "I have several options for you!"
If you are a greying client, be reminded that your regrowth will be more prominent if you go darker. The contrast between light and dark is greater than light on light. However, you may be more comfortable in darker shades, but you can still add a few highlights through the top which helps break-up the appearance of your regrowth.
If you decide to go lighter, which many people do, I recommend using a highlight effect all over because you'll blend the greys away subtly (as you see with my color client in this post), and the lightness off the greys will actually blend nicely into the blonding effect. I have greying clients that only want highlights and no base color because they love the subtle effect and blending of the highlights into their natural color.
Be sure you are working with the best hair color professional around. Ask around, look at photos for inspiration, and have some fun.