afaik the carcols for the pranger and most other base game cars is located in mods\update\update.rpf\x64\data. The file is actually carcols.ymt not .meta like dlc and modded cars. OpenIV cant open .ymt files but if you extract them you can edit them normally with notepad++. A thing to note is that the pranger uses sirensettings "1", which is used by most other police cars, so if you modify the colors of this it will change other police cars too. What you can do (I believe but never tried myself) is open carvariations.ymt (located in the same directory) change the pranger's sirensettings to a value that isnt used by anything, then go to carcols, copy all the lines for sirensettings "1", paste them then change the sirensettings value to the one you chose for the pranger, then finally you can edit the color values to what you want without messing up other police cars.