var colors = new [] {Color.black, Color.green, Color.yellow};

foreach (Transform t in GameObject.Find("/Platforms").transform) {

    t.GetComponentInChildren<Renderer>().material.color = colors[Random.Range(0, colors.Length)];

}

platformRandom.GetComponentInChildren<Renderer>().material.color = Color.black;

int[] numCol = new int[3] { 1, 2, 3 };

        for (int i = 0; i < numCol.Length; i++)
        {
            t = numCol[Random.Range(0, numCol.Length)];
        }

platformRandom = GameObject.Find("Platform 7_1 (1) (Clone)");