Fix color in the preview fragment (2/2)

Colors were inconsistent between the preview fragment and the actual
wallpaper colors set, because the style was not accounted for.
Adjust to account for style when changing the colors of the preview
fragment UI. Style-related changes are included in ThemePicker while
PreviewFragment changes are in WallpaperPicker2.

Flag: NONE
Bug: 308947090
Bug: 308946897
Test: manually verified with different wallpapers
Change-Id: I1897ae1e18113fdbfa573676111ccf3b1daee82f