theme(meltbus): Adapt vterm colours to match user's expectations

vterm abuses the background colour of the first eight colours to
generate the upper eight colours.

themes/doom-meltbus-theme.el

@@ -346,14 +346,14 @@ highlight interactive elements."
    (treemacs-git-conflict-face :foreground vc-conflict)
    (treemacs-git-modified-face :foreground vc-modified)
    ;;;; vterm
-   (vterm-color-black :inherit 'term-color-black)
-   (vterm-color-red :inherit 'term-color-red)
-   (vterm-color-blue :inherit 'term-color-blue)
-   (vterm-color-green :inherit 'term-color-green)
-   (vterm-color-yellow :inherit 'term-color-yellow)
-   (vterm-color-magenta :inherit 'term-color-magenta)
-   (vterm-color-cyan :inherit 'term-color-cyan)
-   (vterm-color-white :inherit 'term-color-white)
+   (vterm-color-black :inherit 'term-color-black :background base3)
+   (vterm-color-red :inherit 'term-color-red :background (doom-lighten red 0.3))
+   (vterm-color-blue :inherit 'term-color-blue :background (doom-lighten blue 0.3))
+   (vterm-color-green :inherit 'term-color-green :background (doom-lighten green 0.3))
+   (vterm-color-yellow :inherit 'term-color-yellow :background (doom-lighten yellow 0.3))
+   (vterm-color-magenta :inherit 'term-color-magenta :background (doom-lighten magenta 0.3))
+   (vterm-color-cyan :inherit 'term-color-cyan :background (doom-lighten cyan 0.3))
+   (vterm-color-white :foreground (doom-darken base8 0.1) :background base8)
    ;;;; which-key
    (which-key-key-face :foreground base5)
    (which-key-group-description-face :foreground base5)