Updated GTK3 list-model color storage and GtkCellRendererText foreground properties to use RGBA values in the user list, notify list, and DCC views while retaining GTK2 behavior.
Copied palette RGBA values before initializing the GTK3 color chooser dialog to ensure RGBA usage on the GTK3 path.
Copy RGBA values from the GTK color chooser into palette entries for the setup dialog path.
Added RGBA-aware list-store color helpers and usage for userlist, notify, and DCC views to keep color handling consistent across GTK versions.
Updated setup color selection and styling to use RGBA-aware GTK3 overrides/CSS while preserving GTK2 behavior in guarded paths.
Switched tree view color models/renderers and other palette consumers (user list, notify, DCC, menus, spell entry, input style) to RGBA-aware types/properties with shared RGB16 conversion usage.
This is the first step to build with GSEAL_ENABLE
setup.c uses a deprecated fontchooser,
chanview-tabs.c didn't like the conversion, and
I am waiting to do some work on xtext.c before
converting it.
