Arnold aiUserData

Since the version 4.7, we can use the Arnold aiUserData which give us the tool can randomize color attribute of a shader color input.

Workflow

Please refer below link and understand what is the 

https://support.solidangle.com/display/arnsupp/2013/01/16/Using%20the%20aiUserData%20shaders

Create an extra attribute to add user data to a shape node (the shape node, not the transform node :)

Select the shape node, and add an extra attribute using the naming convention "mtoa_constant_". For example, an attribute named "mtoa_constant_MyRed" would add the user data "MyRed" to the shape node.

_{add attribute to shape node, notice the naming convention: mtoa_constant_XXX}

Add an aiUserData node to a shading network and connect it.

In the aiUserData shader attributes, set Float Attr Name to the name of the user data.

For example, if you added an attribute named "mtoa_constant_MyRed", then set Float Attr Name to "MyRed".

_{add attribute to aiUserData node, notice the naming convention:  mtoa_constant_}XXX, only XXX

Miarmy Special Recipe

In Miarmy render, we can randomize these values.