You can change the color of an object with a very simple C# script on the object.
First the quick and dirty solution to make an object red:
GetComponent<Renderer>().material.color = Color.red;
This changes the first color property of the first material of the object to RGB
#ff0000. When you would like to set a specific color property of a specific material, check out
Why is this solution dirty? Because what it actually does internally is to create a complete copy of the material, then change the color value on it and then assign the new material to the object. This is not just slow, it also means that the object now has an own material and no longer shares its material with all other objects which use the same material asset.
A far more elegant solution is to use a material property block:
MaterialPropertyBlock props = new MaterialPropertyBlock();
When you set a property block, the material assigned to the object stays unchanged, but the renderer of this game object overrides its settings with those set on the property block.