Lights reset to white in certain cases.
In some cases lights reset to white after configuration.
1: When you building a craft and configure lights, turn them on to check the lights in the editor and then reload the craft, they will reset to white in the editor after you reload the craft.
2: If you don't check the lights (don't turn them on) and reload the craft they will not reset to white, but only in the editor. They will reset to white when you launch the craft afterwards.
The only way to get them to not reset is to configure them and then launch the craft immediately or leave them on and save the craft with the lights on, then it will also not reset on launch.
Applies to all lights, even on the landing gear.