FPSCounter

using UnityEngine;
using UnityEngine.UI;

[RequireComponent(typeof(Text))]
public class FPSCounter : MonoBehaviour {

    [HideInInspector]
    public float fps = 0.0f;
    public float updateRate = 4;

    private Text outputText;
    private int frameCount = 0;
    private float dTime = 0.0f;
    private string textColor {
        get {
            if(fps <= 15f)
                return "red";
            if(fps <= 25f)
                return "orange";
            if(fps > 50f)
                return "lime";
            return "";
        }
    }
    private string formatedText {
        get {
            return "FPS: <color=" + textColor + ">" + fps.ToString("00.0") + "</color>";
        }
    }

    void Start() {
        outputText = GetComponent<Text>();
    }

    void Update() {
        frameCount++;
        dTime += Time.deltaTime;
        if(dTime > 1.0f / updateRate) {
            fps = frameCount / dTime;
            frameCount = 0;
            dTime -= 1.0f / updateRate;
        }

        outputText.text = formatedText;
    }
}