It might be your carvariations.meta file...
Search for carvariations.meta in OpenIV
Locate the vehicle name that is giving you issues
It might look something like this:
<modelName>police4</modelName>
<colors>
<Item>
<indices content="char_array">
0 <-- primary color
0 <-- secondary color
11 <-- This is your pearlescent setting
156
0
0
Try changing your pearlescent # setting