Identification of objects in ref_ovl = TRUE plot

[HAB1990]

when using the ref_ovl = TRUE function to show only meaningful results, and when using a second object, it can be very hard to see whether the effects are from the first or second object, because there is no distinction in colour. For example when only object 1 has a meaningful effect, there will only be one visible line for that parameter, but it can be difficult to see whether that effect is linked to the first or second object (you have to start interpreting the height / position of the line). Is there any reason for why the ref_ovl shading cannot be done using the black / red colour cording (or some other kind of identification of objects)?