I noticed when trying to set an Ambient Light custom color using the color picker, the ambient light on the map didn't update immediately. Either I had to toggle Ambient Light off/on, zoom the map in/out, or reopen the map. However, the Ambient Light presets update immediately.

To recreate in a new 5E campaign:
  1. Create a new image
    • I just created directly from Assets > ForestFloorGrass_background_decoration_8x8.png with the Create Image Record button
  2. Enable Lighting
  3. On Lighting tab, select Ambient Lighting and then set the Ambient Light preset to Dawn. The Ambient Lighting on the map displays immediately as expected
  4. Click Color and select a different color. Ambient lighting does not update immediately
    • Toggling ambient light off/on, zooming the map in/out, or reopening the image will cause it to update

FGU v4.2.1
5E v2022-04-09