In this tutorial we are going to create a chrome material in Vray. We will start by creating a chrome effect, and then we'll try to add different colors to it's chrome. We'll end this tutorial by making a rainbow chrome material.
Make sure you are using Vray as your render engine. Once you've learned the technique, you can do it in other render engines as well. Open Material editor and apply VRayMtl to one of the free sample slots. Name it as you wish. I've chosen Chrome.
Change Diffuse Color to black. Reflect Color to White. Make Sure Fresnel reflections is turn on. Change Fresnel IOR to 20.
Apply this material to your object and render your scene. We already made a chrome material.
To change the color of the chrome, you do not need to change the Diffuse color. As chrome is type of metal, you should change its reflection color. Here I changed Reflect color to red.
To make a rainbow color, the reflection color also needs to be changed. But how to make rainbow color? We will use Falloff map and Gradient map to create this effect. First add Falloff map to the Reflect map slot.
In Falloff Parameters, change both Front and Side color to White. Then add Gradient map to both color slots. Note that if you want to create car paint material, you can just change Front and Side color. For example, yellow for Front color and darker yellow(or orange) for Side color.
In the Front Gradient parameters, change 3 colors to Green, Blue and Violet.
In the Side Gradient parameters, change 3 colors to Red, Orange and Yellow.
Now you can render your scene. Note that you can choose other colors.
The last tip is how to perfect the reflection on the chrome material. You may have seen that reflection on shiny surfaces such as metal and chrome are not perfectly a "mirror-like" model, and have some noises and waves, to create that wavy effect, you can add Noise map to the Bump slot. Change the noise size to fit on your model and make sure you are using a small value on your Bump. I chose 1 for this scene. In the below photo you can compare the render with and without Noise effect.