Renault web configurator how to get the same result with render passes

[yuri_ch]

Hi! I'm planning to add to my site some product which user can interactively rotate and I'd like to add an opportunity for the user to choose paint colours of it. Instead of rendering a huge amount of images for each color, I want to do the same as it has been done on Renault official site. Here is .psd file attached with an image from here. As you can see this transparency got all shadow, reflection and specular information, so if you add some colour under the layer with the car you can change the colour of it and it looks great.
The image was taken from Renault official site. It is used with an interactive web configurator. Does anybody know how to prepare the same thing in Keyshot and Photoshop? Thanks!

[csar]

What you must do is in the render settings, select as the type of PSD file (PNG and TIFF also work, files that include alpha channel, transparency). Also select "Render Steps" and select Ambient Occlusion and Shadows (for shadows) and Reflection and Refraction (for highlights and reflections).
In Ps you open the generated image and place the different render steps. You assign the blending mode that best suits each rendering step (multiply for dark layers and screen for light layers). Then you combine those layers of highlights and shadows and you should have a layer like the one in Rault's example