Multiple Colours
If your original texture files are yellow, then you name them as so: 
carnamecolour_region(_dmg)(_ni).bmp
example: 
vppanozmagenta_tp_dmg.tga
   ^      ^     ^  ^
   |       \     \.  `-.
   |        \      \.   `-.
carname      colour region damage

carname: Your car's files' basename - this file is from the panoz gtr-1, so it's vppanoz.
colour: This is the colour's name - magenta
region: tp indicates that this is the top texture of the panoz.
damage: this indicates that the texture is a damage texture.

If you exported this texture as a scheme from ZModeler, you would choose
Replace: white
With: magenta
since white is the panoz's original colour, that is assigned to it in Zmodeler.
For your car, say the colours are:
yellow, black, green, and orange
vpcarnameyellow_side.tga
vpcarnameyellow_side_dmg.tga
vpcarnameyellow_ends.tga
vpcarnameyellow_ends_dmg.tga
vpcarnameblack_side.tga
vpcarnameblack_side_dmg.tga
vpcarnameblack_ends.tga
vpcarnameblack_ends_dmg.tga
vpcarnamegreen_side.tga
vpcarnamegreen_side_dmg.tga
vpcarnamegreen_ends.tga
vpcarnamegreen_ends_dmg.tga
vpcarnameorange_side.tga
vpcarnameorange_side_dmg.tga
vpcarnameorange_ends.tga
vpcarnameorange_ends_dmg.tga You would assign the vpcarnameyellow_side and vpcarnameyellow_end textures to your car, but have the rest in your car's textures folder. You go to export, select multiple colours. Delete the one that's already there. Now type into the top box, yellow. Into the bottom box goes black. Click add to list button. change the bottom box to green, click add again. Change it to orange, and click add again. click export.

Now, go to your carname.info file. Go to the part that says "Colors=". Change this to "Colors=Yellow|Black|Green|Orange". Put the "|" in between each of the colours, to indicate where the names change. This is done because some cars have names with spaces in them. Something to note is that you can't have more than 110 or so characters in this line. So, for example, "Colors=Yellow with red spots|Orange with green cows|Blue tinted with a hint of purple|Gold and Green striped|Red and black, with white will not work. 1