How would I change lightbar colors in Zmodeler3?

I have just recently decided to attempt to make an ELS vehicle in Zmodeler 3.

The vehicle I want to make is not going to be a police car, but rather a staff vehicle. Because it isn’t a police vehicle, I want the lights on the light bar to be different colors than red and blue. For example, green and purple.

I downloaded a lightbar from lspdfr. The lightbar came with two files. A textures.png file and then a lightbar.z3d file. The textures file shows the lights and actual design of the lightbar so I attempted to edit the colors in that file but when I tried to test it by merging the lightbar with a vehicle in zmodeler the lights were still red and blue, so changing the textures.png did nothing.

So because I am very new to Zmodeler, I have no idea how I could actually change the light colors and I was hoping that somebody here who is more experienced with Zmodeler might be able to help me. Thanks in advance.