DropDown changes background color with selected option

Hi there!

I´m stuck with this DropDown which I need to have a red background if the option TBD is active (which is the default option) and to have no backgrond if any other option is selected.

The red background is a red rectangle that it is visible or hidden, I have tthis code in the change event of the DropDown:

if (this.rawValue == "TBD"){    RectangleRed2.presence = "visible";
}else{    RectangleRed2.presence = "hidden";
}

But the thing is that the event checks the value when is changed, so if I am in TBD value and I selec Item 1, the recntagle is still visible, because at the moment I selected the Item 1 the value was TBD,  so is not working the way I need it to.

Anys Ideas?

Thanks!