You can add a Post Process Volume to your level and size accordingly, or set to unbound in the details panel if you want it to be your entire level. In your level blueprint, you can get a reference to the Post Process Volume and get settings from that volume. You should then be able to break Post Process Settings (a HUGE node) and then change a particular setting then make Post Process Settings and reapply to the volume. This should allow you to change the color as you need.