Han is correct. This is by design.
Most controls have different default colors when they are in indicator mode as they do in other modes. Therefore, if (and only if) your panel is in "Conform to system colors" mode, these controls will have their default colors reapplied whenever you change to or from indicator mode, in the same way as if you had just turned on the ATTR_CONFORM_TO_SYSTEM panel attribute.
If you don't want this behavior, and you don't create new controls programmatically after your panel is loaded, I think you can simply turn off ATTR_CONFORM_TO_SYSTEM after loading the panel (since once the panel is loaded, it's really no longer needed). This way, the controls won't reset their colors when you change the mode.
Luis
NI