There is rarely one right answer. Here are several categories of pairing options, each with a reason it may work.
Denim Blue
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Sapphire
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Cobalt Blue
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Payne's Grey
Similar lightness for a subtle, tone-on-tone pairing with minimal contrast.
Royal Blue
Enough lightness contrast to read as two distinct colours without feeling harsh.
Steel Blue
Enough lightness contrast to read as two distinct colours without feeling harsh.
Slate Blue
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.
White
Strong lightness contrast and saturation for a bold, graphic pairing.
Mint Cream
Strong lightness contrast and saturation for a bold, graphic pairing.
Off-White
Strong lightness contrast and saturation for a bold, graphic pairing.
Ivory
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.
Gold
A saturated accent from a different hue family for a deliberate pop of contrast.
Citrine
A saturated accent from a different hue family for a deliberate pop of contrast.
White
Meets WCAG AA contrast (7.2:1) for normal text if used as text/background.
Ivory
Meets WCAG AA contrast (7.1:1) for normal text if used as text/background.
Mint Cream
Meets WCAG AA contrast (7.0:1) for normal text if used as text/background.
Azure
Meets WCAG AA contrast (7.0:1) for normal text if used as text/background.