Folders on the LG device's home screen have a white, slightly transparent background by default. The folder color can be adjusted to 11 other colors in the options. Unfortunately, you can't choose your own color for the LG.

Android 9 | LG UX 9.0
Step 1:  Open desired  Folder
Step 2:  Tap on  Folder name
Step 3:  Choose desired  Color
Step 4:  Confirm with  OK
  1. Open desired Folder
  2. Tap on Folder name
  3. Choose desired Color
  4. Confirm with OK

LG Instructions