[Bug]: App toolbar invisible on dashboard app when background image is white

[PVince81]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

The app header is invisible in the dashboard app when using a white background:

Steps to reproduce

1. Go to the theming section
2. Set the theme color to #C96C42
3. Upload this unsplash image as login page image: https://unsplash.com/photos/25gENtMQcxk
4. Log in and go to dashboard

Expected behavior

It seems the top bar is supposed to adjust itself to the colors somehow but failed to do so.

Installation method

Other

Operating system

No response

PHP engine version

No response

Web server

No response

Database engine version

No response

Is this bug present after an update or on a fresh install?

No response

Are you using the Nextcloud Server Encryption module?

No response

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

Enabled:
  - activity: 2.16.0
  - cloud_federation_api: 1.8.0
  - comments: 1.15.0
  - contactsinteraction: 1.6.0
  - dashboard: 7.5.0
  - dav: 1.23.0
  - federatedfilesharing: 1.15.0
  - federation: 1.15.0
  - files: 1.20.0
  - files_automatedtagging: 1.14.0
  - files_external: 1.17.0
  - files_sharing: 1.17.0
  - files_trashbin: 1.15.0
  - files_versions: 1.18.0
  - lookup_server_connector: 1.13.0
  - nextcloud_announcements: 1.13.0
  - notifications: 2.12.0
  - oauth2: 1.13.0
  - photos: 1.6.0
  - provisioning_api: 1.15.0
  - recommendations: 1.3.0
  - serverinfo: 1.14.0
  - settings: 1.7.0
  - sharebymail: 1.15.0
  - survey_client: 1.12.0
  - systemtags: 1.15.0
  - theming: 2.0.0
  - twofactor_backupcodes: 1.14.0
  - updatenotification: 1.15.0
  - user_status: 1.5.0
  - viewer: 1.8.0
  - weather_status: 1.5.0
  - workflow_script: 1.6.0
  - workflowengine: 2.7.0
Disabled:
  - admin_audit
  - bruteforcesettings
  - calendar
  - contacts
  - email_template_example-0.0.1
  - encryption
  - files_3d
  - files_accesscontrol
  - files_antivirus
  - files_downloadlimit
  - files_retention
  - files_texteditor
  - files_versions_s3
  - groupfolders
  - guests
  - mail
  - music
  - officeonline
  - password_policy: 1.14.0
  - previewgenerator
  - ransomware_protection
  - registration
  - richdocuments
  - shareimporter
  - sharepermissions
  - spreed
  - support: 1.7.0
  - suspicious_login
  - terms_of_service
  - testing
  - twofactor_totp
  - user_ldap
  - user_migration
  - user_saml

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

Observed on git master 4f55ba2

[joshtrichards]

Duplicate of #28649