Thanks for reporting the problem when in dark mode. I'll look into it.
As to the yellow warning "badge" on the Tunnelblick icon, it is "incongruous" by design. It is supposed to draw your attention. If you want it to go away, fix the underlying problem(s) that the warnings are about, or check "Do not warn about this again" before clicking the "OK' button.
(The yellow triangle isn't an asset inside of Tunnelblick, it's a system asset. Tunnelblick gets it using NSFileTypeForHFSTypeCode(kAlertCautionIcon), then draws it on the Tunnelblick icon before displaying the Tunnelblick icon. It's done that way because
the user can specify a custom icon and we want to "badge" any icon that is used.)