How to apply different materials to spawned chracters?

I use a script for spawning characters and I want each character to use a different material, so all of they look different. Materials are stored as a jpg files in my projects.
What are the ways to make this work?

 IEnumerator InstanceSpawner()
        yield return new WaitForSeconds(0);
        while (!stop)
            RandomHuman = Random.Range(0, 2);
            Vector3 SpawnPosition = new Vector3(Random.Range(-SpawnValues.x, SpawnValues.x), 1, Random.Range(-SpawnValues.z, SpawnValues.z));
            Instantiate(humans[RandomHuman], SpawnPosition + transform.TransformPoint(0,0,0), Quaternion.Euler(0,90,0));
            yield return new WaitForSeconds(SpawnWait);

Did u find the solution yet?

Instantiate returns a reference to the new object.
GameObject newHuman = Instantiate(....);
Then, you can use GetComponent() to get a component you want. Often, you’re using a MeshRenderer component to color the object. So,

MeshRenderer meshRenderer = newHuman.GetComponent<MeshRenderer>();

Then get at its color.

meshRenderer.material.color = Color.Blue;