Transparency determines how the texture will blend with the paint colour.
Blank.png is a completely blank texture, which means the vehicle will be coloured the same as your paintcan. Black25, 50, 75 are transparent textures with light to dark tint, which will result in darker surfaces when applied on the model.
In short; it does.
Note: When you are making a model with transparent and non-transparent textures in blender, make sure to put those parts into different objects, as the transparent textures "bleed" paint colour, which results in oddly coloured models when the shaders have been turned off.