It's probably the image file that you're using. Make sure the file is uncompressed and also that it's a power of 2 (eg, 2x2, 4x4, 8x8, 16x16, 32x32, 64x64, 128x128, 256x256, 512x512.....)
It it's showing up white in Trainz, then it's most probably a texture problem. Also, if you're reskinning, make sure that the image file that you're using has the same name as the original image file.
Mike