One Commander themes are completely independent of Windows themes and colors, so that user can have a complete control over look of One Commander. If you open Nord.xaml from Themes folder you will see on line 60 for Tint color:
<Color
x:Key="WindowAcrylicTintColor"
A="255"
R="48"
G="52"
B="63"/>
so it is bluish tint.
You can create a folder like Nord2 next to Nord, copy the nord.xaml to the new folder, and edit it to any RGB color you like. Save, select that theme in OC, and press ctrl+shift+F5 (or restart program)
On my monitor in AdobeRGB color space I can't see blue tint, even when content behind window is white, but it should be slightly according to those values.