Settings portal doesn't work with automatic accent color

[alice-mkh]

What Happened?

Basically if set to automatic we just return black color instead, which is not that great.

Steps to Reproduce

1. Set accent to automatic
2. Open any non-elementary app that supports fdo accent color (e.g. nightly gnome apps)

Expected Behavior

It should just follow the same color elementary apps use

OS Version

7.x (Horus)

Software Version

Compiled from git

Log Output

No response

Hardware Info

No response

[alice-mkh]

There is relevant code for that in AccentColorManager, but the problem is that the portal is a separate binary atm. They can be merged, but it's messy.

A simpler (tho less robust) way is to have portal listen to gtk-theme instead and check the name. I can open a MR, but wanted to make sure it's fine here.

[danirabbit]

@alice-mkh sorry for not following up sooner! I think that sounds like an acceptable way to get this working right away and we can reconsider as we revisit accent colors in OS 9. Thank you!