Random Color Control Question

Hello, I am trying to do and understand something. For my cars, I want to limit their colors to 8 color options. Also, I am trying to understand the relationship between the "Col" and "is_random" color attributes. I don't understand how Blender is looking at one or the other to determine what color to produce. It would make sense, based on setting the color of the color attribute "is_random" to a value of .4 and the shader using whatever is set to a value color of .4 on the object to present whatever color nodes are used in association with "is_random", but I'm not sure that's how the relationship works. I have two node sets to present. The top one will be the color swatch randomization group eventually, and the portion to the right is how I'm trying to connect it into the gradiant and edge highlight groups. The attribtutes below are what I'm trying to understand how to connect to make them function as I'm imagining. The first group has the vehicles acting as I want, but the bench is also acting as if it has the "is_random" color attribute associated with it, which they do not. So next I tried to use the hue saturation value node as in the tutorial, at which point the benches worked again but the vehicles do not. Any thoughts as to how I can get them to function properly within the same shader?nodes 1.pngnodes 2.png