There is rarely one right answer. Here are several categories of pairing options, each with a reason it may work.
Tourmaline
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Dark Olive Green
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Dark Slate Grey
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Sea Green
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Storm Grey
Enough lightness contrast to read as two distinct colours without feeling harsh.
Grey
Enough lightness contrast to read as two distinct colours without feeling harsh.
Moss Green
Enough lightness contrast to read as two distinct colours without feeling harsh.
Slate Grey
Enough lightness contrast to read as two distinct colours without feeling harsh.
Magenta
A saturated accent from a different hue family for a deliberate pop of contrast.
Fuchsia
A saturated accent from a different hue family for a deliberate pop of contrast.
Purple
A saturated accent from a different hue family for a deliberate pop of contrast.
Ruby
A saturated accent from a different hue family for a deliberate pop of contrast.
White
Meets WCAG AA contrast (7.5:1) for normal text if used as text/background.
Ivory
Meets WCAG AA contrast (7.4:1) for normal text if used as text/background.
Mint Cream
Meets WCAG AA contrast (7.3:1) for normal text if used as text/background.
Azure
Meets WCAG AA contrast (7.3:1) for normal text if used as text/background.