Terminal reports incorrect background color

[bash]

Cosmic version: 77be96e

When querying the terminal for its background color
using OSC 11 it always reports black (^[]11;rgb:0000/0000/0000^[\) instead of a dark gray in dark mode and light gray in light mode.

This breaks tools that try to detect dark/light mode based on the
terminal's background color. Some of these tools are: git-delta, run0 (systemd), and bat.

Steps to reproduce:

• Enable light mode (View -> Settings -> Theme -> Light)
• Run printf '\x1b]11;?\e\\' && cat -v

Note: The foreground color (OSC 10) seems to be reported correctly.