ikhal: Unreadable colors for agenda selection in new event

Describe the bug
With the light color theme, agenda selection is done with a black background which makes agenda names unreadable (see attached picture)

If applicable: Stack Trace
N/A

To Reproduce
Steps to reproduce the behavior:

[calendars]
  [[pda]]
    path = ...
    color = dark blue

....
[view]
  theme = light

Expected behavior
Agenda selection menu should use a light background for names.

Screenshots

OS, version, khal version and how you installed it:

• The output of khal --version: khal, version 0.11.3.dev206+g4b6e7991
• Installation method: git
• python version: Python 3.12.3 (main, Apr 10 2024, 05:33:47) [GCC 13.2.0] on linux
• OS: Linux vagabond 6.8.0-31-generic 31-Ubuntu SMP PREEMPT_DYNAMIC Sat Apr 20 00:40:06 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
• Your khal config file: see above
• The versions of your other python packages [e.g. the output of pip freeze]:

atomicwrites==1.4.1
click==8.1.7
click-log==0.4.0
configobj==5.0.8
icalendar==5.0.12
-e git+ssh://git@github.com/pdav/khal.git@4b6e79912eca9c3fcba8415d4e0c18d87e9d13f4#egg=khal
python-dateutil==2.9.0.post0
pytz==2024.1
pyxdg==0.28
six==1.16.0
typing_extensions==4.11.0
tzlocal==5.2
urwid==2.6.12
wcwidth==0.2.13

Additional context
N/A

Reproduce the issue in khal's agenda selection menu using the supplied [calendars] and light [view] theme configuration. Trace the agenda-selection rendering and theme handling; done means agenda names remain readable with a light background in the light theme.