The "Blipz" toolbar button has a different color than other buttons while using all the Firefox themes

[Softvision-AndreeaCupsa]

[Affected versions]:

• Firefox Release Unbranded 63.0.1
• Firefox Beta Unbranded 64.0b7

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have the following prefs:
  • extensions.legacy.enabled to true
  • xpinstall.signatures.required to false
  • xpinstall.signatures.dev-root to true
  • extensions.webcompat-blipz-experiment.variation to any branch variation except control
• Have the Webcompat Blipz Experiment installed from here

[Steps to reproduce]:

1. Open the Firefox browser with the profile from the prerequisites.
2. Navigate to google.com and press the "Shift + Alt + P" keys.
3. Observe the "Blipz" toolbar button.

[Expected result]:

• The button has the same grey color as the other buttons.

[Actual results]:

• The button is almost black.

[Additional Notes]:

• The "Blipz" toolbar button has different colors than the other buttons on all themes: Default, Dark and Light ones.
• Please see the following page related to Photon iconography: https://design.firefox.com/photon/visuals/iconography.html
• Attached screenshots with the issue:

[wisniewskit]

This doesn't seem like a big enough issue to block on for v2, but it's definitely something we want to polish in the future.