I have a platform ramp exported from blender into TRS2019. When I rotate it in surveyor it reaches a point where in turns very dark. No other objects that I have created do this. It was made using the mirror modifier in Blender. It looks fine in asset previewer through 360 degrees.
What you see in a 3d-prog may not always be the same as trainz shows
can you check normals in Blender? if it were a gmax, I'd check for flipped normals.
an alternative for mirror, often can be a copy/clone, move and rotate 180 degrees
greetings GM
