changing color of sprite not every frame

Question

So I have been trying making this game, which changes color of sprites in it. It should only happen when OnMouseDown(). but it is executing every frame and cannot go out of the couroutine. I want the color change to be slower. Please mark the colors should still change.

Please Help,

public class control : MonoBehaviour
{
    public bool startstop = false;
    SpriteRenderer m_SpriteRenderer;
    private void Update()
    {
        StartCoroutine("Changecolor", 3f);
    }
    IEnumerator Changecolor()
    {
        yield return new WaitForSeconds(3);
        if(startstop == true)
        {
            int random = Random.Range(1, 4);
            if (random == 1)
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.blue;
            }
            else if(random == 2)
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.red;
            }
            else if(random == 3)
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.green;
            }
            else
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.yellow;
            }
        }
    }
    private void OnMouseDown()
    {
        startstop = !startstop;
    }
}

Answer 1

All you need to do here is move your if statement into the Update function. In your case you would be calling the co routine every frame, and there would be a lot off calls waiting for those 3 seconds to pass and then once the startstop is true, a lot of them would be called. So here, you basically only call it once the startstop is true, and then you immediately change its value to false so no more than 1 call is executed.

public class control : MonoBehaviour
{
    public bool startstop = false;
    SpriteRenderer m_SpriteRenderer;
    private void Update()
    {
        if(startstop){
            StartCoroutine("Changecolor", 3f);
            startstop = false;
        }
    }
    IEnumerator Changecolor()
    {
        yield return new WaitForSeconds(3);
            int random = Random.Range(1, 4);
            if (random == 1)
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.blue;
            }
            else if(random == 2)
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.red;
            }
            else if(random == 3)
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.green;
            }
            else
            {
                m_SpriteRenderer = GetComponent<SpriteRenderer>();
                m_SpriteRenderer.color = Color.yellow;
            }
    }
    private void OnMouseDown()
    {
        startstop = !startstop;
    }

Answer 2

The other way would be looping the coroutine instead of calling it multiple times, and stopping it when needed.

public class Control : MonoBehaviour
{
    public bool startstop = false;
    SpriteRenderer m_SpriteRenderer;

    IEnumerator Changecolor() {
        yield return new WaitForSeconds(3);
        int random = Random.Range(1, 4);
        if (random == 1) {
            this.m_SpriteRenderer = this.GetComponent<SpriteRenderer>();
            this.m_SpriteRenderer.color = Color.blue;
        } else if (random == 2) {
            this.m_SpriteRenderer = this.GetComponent<SpriteRenderer>();
            this.m_SpriteRenderer.color = Color.red;
        } else if (random == 3) {
            this.m_SpriteRenderer = this.GetComponent<SpriteRenderer>();
            this.m_SpriteRenderer.color = Color.green;
        } else {
            this.m_SpriteRenderer = this.GetComponent<SpriteRenderer>();
            this.m_SpriteRenderer.color = Color.yellow;
        }

        this.StartCoroutine("Changecolor", 3f);
    }

    private void OnMouseDown() {
        if (this.startstop) {
            this.StartCoroutine("Changecolor", 3f);
            this.startstop = !this.startstop;
        } else {
            this.StopCoroutine("Changecolor");
            this.startstop = !this.startstop;
        }
    }
}

If this doesn't work you could fix it easily, as I'm at work and cant test it right now ^^