There is rarely one right answer. Here are several categories of pairing options, each with a reason it may work.
Graphite
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Charcoal
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.
Petrol Blue
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Black
Enough lightness contrast to read as two distinct colours without feeling harsh.
Persian Blue
Enough lightness contrast to read as two distinct colours without feeling harsh.
Payne's Grey
Enough lightness contrast to read as two distinct colours without feeling harsh.
Cobalt Blue
Enough lightness contrast to read as two distinct colours without feeling harsh.
Tomato
Strong lightness contrast and saturation for a bold, graphic pairing.
Vivid Coral
Strong lightness contrast and saturation for a bold, graphic pairing.
Saffron
Strong lightness contrast and saturation for a bold, graphic pairing.
Royal Blue
Strong lightness contrast and saturation for a bold, graphic pairing.
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.
Lime
A saturated accent from a different hue family for a deliberate pop of contrast.
Gold
A saturated accent from a different hue family for a deliberate pop of contrast.
White
Meets WCAG AA contrast (12.7:1) for normal text if used as text/background.
Ivory
Meets WCAG AA contrast (12.6:1) for normal text if used as text/background.
Mint Cream
Meets WCAG AA contrast (12.5:1) for normal text if used as text/background.
Azure
Meets WCAG AA contrast (12.4:1) for normal text if used as text/background.