One could try darkening the “white” one step at a time to determine if there is a treshold in Vissim when this kicks in. Rendering applications often have issues with pure, full white. The whitest white paint you can buy is somewhere in the 245,245,245 range.
A couple of possibilities, and a suggestion…
The image still looks like it would if it is not lit from the front. You could look for any ambient light setting in the program, and increase that value.
Some programs take a limited range of colors, from 16,16,16 to 235,235,235, but I don’t think that is the case here, because you are showing 153,153,153. Which is very low.
What happens if you fill the letters with a material, which is a bitmap that is white? That ought to rule out whether the program is misreading the color values.
My guess is still on the ambient light settings.
Unfortunately, Vissim does not have any ambient light settings, so I can’t adjust that. I filled the letters with white material and I still have the same issue in Vissim. I’m assuming it’s an issue within Vissim. I also played with different shades of white for the letters and Vissim still shows them as being gray. I’m going to try to make the street sign in 3DS Max and import it into Vissim. If Vissim changes the color of the letters, then I’ll know that Vissim is the culprit.
Have you tried rotating the sign so it faces toward your light source? Honestly, to me, it looks like a white surface that is not receiving direct light.
Vissim is a software to model traffic, so it does not have options to adjust any imported 3d models other than scale and rotate. If you scroll up, you’ll see a screenshot of the street sign facing forward.