There is rarely one right answer. Here are several categories of pairing options, each with a reason it may work.
Grey
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Storm Grey
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Slate Grey
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Dusty Lavender
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Mushroom
Enough lightness contrast to read as two distinct colours without feeling harsh.
Silver
Enough lightness contrast to read as two distinct colours without feeling harsh.
Lilac
Enough lightness contrast to read as two distinct colours without feeling harsh.
Ash Grey
Enough lightness contrast to read as two distinct colours without feeling harsh.
Taupe Grey
A low-chroma neutral lets the original colour stay the visual focus.
Grey
A low-chroma neutral lets the original colour stay the visual focus.
Silver
A low-chroma neutral lets the original colour stay the visual focus.
Ash Grey
A low-chroma neutral lets the original colour stay the visual focus.
Cyan
A saturated accent from a different hue family for a deliberate pop of contrast.
Lime
A saturated accent from a different hue family for a deliberate pop of contrast.
Yellow
A saturated accent from a different hue family for a deliberate pop of contrast.
Chartreuse
A saturated accent from a different hue family for a deliberate pop of contrast.