Don't know if you fixed this in your recent update, but from the pictures it seems like your map is either lacking a
light_environment or needs a higher brightness.
You can look
HERE for settings for light_environment used in official maps/skyboxes.
Personal opinion here: I find it best to look at the light entities and settings used in decompiled maps you can find
HERE on site. Usually the light_environment is coupled along with a
shadow_control,
env_tonemap_controller,
env_fog_controller, and a logic_auto (to send inputs to the tonemap controller) in all maps. But that's getting into the more advanced lighting options that you won't need until betas.
For simplicity's sake I tend to use/copy the settings for those entities in decompiled valve maps that share a lighting style I want. This allows me to spend a lot less time on lighting when trying to get a layout going in an alpha.