bg-blue colour used in example is missing 2 years ago

From Russell Sim to ~protesilaos/modus-themes

Hey,

Love the update, I was one of the users of the retro box blue highlight
that was once an option.  It took a bit of fiddling to get a replacement
but I like the flexibility the new version has.

However, when I was experimenting I found a bug in this example.

--8<---------------cut here---------------start------------->8---
;; Blue background, neutral foreground, intense blue border
(setq modus-themes-common-palette-overrides
      '((bg-mode-line-active bg-blue)
        (fg-mode-line-active fg-main)
        (border-mode-line-active blue-intense)))