This is a common issue, especially if you are using a replace slot, or using a sample vehicles.meta entry.
Depending on how you have installed your vehicle, you should find the vehicles.meta file that applies to that vehicle. If you used Albo’s Modding DLC Pack 5, you can find that information in the Read Me file.
Use CTRL + F to search for the model and find the following entry:
You should then edit that entry to look like it does below.
<diffuseTint value="0x00FFFFFF" />
If you have any further issues, give us a shout in our Discord and we’ll try and help you out.