About the tracks: if you contact the manufacturer, I'm sure they can help you solve the construction problem.
About the weld bead: the problem lies in that the color of the model is 4 color (offset?) printed on white stock to obtain the OD ground. It is made of magenta, cyan, yellow & black on a white ground. The white influences the printed color because the ink is not laid down opaque. Paint is OD pigment, there is no other influencing color(s), and from the looks of it you have laid it down as opaque on a non-opaque coating. You'll never match same color of dissimilar materials. To match you will need to color the entire model with paint.
To obtain what appears as to be a cast lower hull texture you may need to apply a coat of putty. You may need to seal the paper first.
Just my observation.
Sincerely,
Mark