I made a quick "how to"for everyone. Download ALL textures for your selected coaster style from my dropbox, and put them in a folder within the same folder that holds the park files:
then, go to the coaster properties > trains > train 1 color setup tab, and point each of the car textures to the textures that are in the folder that you put the textures in. Only point to the files that are just plain old cartexture_01, cartexture_02 etc. Do this for all of your custom textures for each train.
then, when save and freeze your coaster, it will have the changes in textures stores. if you notice the textures are all grey, except for some parts. whatever is gray is overwritten by the colors you select for the coaster itself in the coaster properties > colors tab.
I have used my generic corkscrew template here to demonstrate how the red stripe was replaced with white. the cartexture names MUST remain constant. If you rename cartexture_01 to Corkscrew_01, the you must also rename the others to Corkscrew_01_coolormap, Corkscrew_01_normalmap, and Corkscrew_01_specularmap.
Let me know if you have any questions!