Init: set accent color from portal feedback

[ryonakano]

Review feedback for #704

I personally think this would even better for readability, but it's fine to close or modify :)

• Keep the update_color method just parses Variant into string representation of color
  • This also makes sure that accent_color is only set in the setup_accent_color method
• Use warning for error message
• Set the fallback color in the catch statement instead of returning the try statement

[danirabbit]

This makes and I agree is better. Thank you!