What you are seeing is the mix of two 'reflections', and the 'texture' of the surface.
The main things you'll need as follows (posting for interested creators mainly ):
*specular. There are 4 obvious specular reflections, these being the front corner of the streamlined 'nose', the front corner of the funnel, the top edge of the side cowling, and the front of the cab.
*Environmental reflections (currently Trainz only supports sky reflections). This gives the overall reflective look to the body. Less reflection on black surfaces in most cases.
*Normals map. This needs to be very carefully made to give the effect you are seeing, since it needs to represent a non-flat sheet metal surface (e.g. all the ripples in the sheet metal), as well as the rivet/bolt/etc details
*Specular map. This will help to change the amount of specular on different parts of the texture, such as reducing it where dirt has built up, or on less reflective colours (e.g. black).
*Carefully made main/diffuse texture. This is the actual visible part, which needs to have some very light shading done to give the impression of the ripples when none of the above are active (e.g. viewed from down low, with the sun at the 'right' angle to now give reflections).
Unfortunately, only the last is really possible when editing an asset that doesn't have the above parts as well. That said, I'm pretty sure the old built-in A4/Mallard model did have a normals map, so a specular map is definitely possible, which could help break up the 'solid' specular effect. However, to create the effects shown in the photos, you definitely need environmental reflections.
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