fix: Adapt the menubar to the primary color if a custom backgorund image has been set

[juliushaertl]

Steps to reproduce:

• Set white as a primary color
• Set a bright background image as the admin
• Disable user theming (personal background image)

Before

App icons where white on white

After

App icons properly adapt to the primary color

[skjnldsv]

Could you also add a use case for this in the cypress tests please?

[szaimen]

This doesnt seem to work if you choose a dark primary color. Also the app title in the heading doesnt seem to be inverted correctly...

[skjnldsv]

We kinda had that discussion with #35482
If we want to apply a different rule following the primary, then we need to apply some overriding variables to the header element

[juliushaertl]

Won't have time looking into that further this week, so If anyone wants to jump in feel free. Otherwise I'll check again somewhen next week.

[MichaIng]

Related: #37379
Avatar and status icon get inverted as well, so it must be taken care that only app icons are inverted.

[skjnldsv]

One tiny comment, but all good otherwise

[skjnldsv]

/backport to stable26

[szaimen]

@skjnldsv the PR hasnt changed since I reviewed it so what shall I review here?

[juliushaertl]

I revived this and pushed a cypress test.

This doesnt seem to work if you choose a dark primary color. Also the app title in the heading doesnt seem to be inverted correctly...

I could not reproduce this anymore

[juliushaertl]

Thinking more about it i don't think this is the right approach, as long as we have no detection or setting for if the background is dark or bright, we can only make it work in either combination. The primary color is only a good indicator for inverting app icons if no background is used. Will close this.