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 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;
    }
}

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;
    }
}