Custom background color does not respect terminal transparency

[Christoph-Harms]

Description:
Defining a custom background color in ~/.config/nchat/color.conf does not respect terminal transparency configuration

Note: This is basically a copy&paste with replacements from hrkfdn/ncspot#1379, as they seem to have the same issue there.

How to reproduce it:

1. Configure terminal to use some level of transparency
2. Open nchat without a custom background color set
3. Observe that, with no custom background color set, the terminal is transparent
4. Set a custom default_color_bg in ~/.config/nchat/color.conf
5. Open nchat
6. Observe that the background is fully opaque

Screenshots
Here is a screenshot of my terminal, running tmux wth nvim on the left, an un-customized nchat in the top right, and nchat with a custom background color in the lower right.

Environment:

• Version: nchat 5.5.6
• OS / distro: Ubuntu 24.04.1

Tested with gnome-terminal and Alacritty, with and without tmux.

[Bellavene]

Same with list border