What i meant was your saturation / fill isn't consistent. Your trucks look like they weren't painted properly, i.e washed out, over sprayed, or bleeding through. I'd suggest selecting the trucks, making them a black and white image and then either using a colorizing tool or a paint bucket fill pick your color, set your alpha (that's how transparant the paint will be applied so as not to loose detail, I use anywhere from 170 to 200 as a value) and adjust the saturation after that. Check the tollerance before you use your bucket fill for color as it doesn't appear the color is being applied to 100% of the texture.
I assume you're after fairly clean looking textures here as would be expected of a special paint scheme locomotive, right?