ChangeColour.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class ChangeColour : MonoBehaviour
{
    public int GoalState = 0; // Any integer between 0 - 2, nogo, target, go respectively
    public Color NoGoColor = Color.red;
    public Color TargetColor = Color.yellow;
    public Color GoColor = Color.green;

    private bool Target = false;
    private bool Go = false;
    private bool NoGo = false;

    private SpriteRenderer[] m_SpriteRenderer = new SpriteRenderer[2];
    private TriggerBoundary mTriggerBoundary;

    // Start is called before the first frame update
    void Start()
    {
        m_SpriteRenderer = gameObject.GetComponentsInChildren<SpriteRenderer>();
        m_SpriteRenderer[0].color = NoGoColor;

        mTriggerBoundary = gameObject.GetComponent<TriggerBoundary>();
        NoGo = true;
    }

    // Update is called once per frame
    void Update()
    {
        switch(GoalState)
        {
            case 0:
                m_SpriteRenderer[0].color = NoGoColor;
                Go = false;
                Target = false;
                break;
            case 1:
                m_SpriteRenderer[0].color = TargetColor;
                NoGo = false;
                Go = false;
                break;
            case 2:
                m_SpriteRenderer[0].color = GoColor;
                NoGo = false;
                Target = false;
                break;
        }
        if (mTriggerBoundary.ColliderIsTriggered)
        {
            m_SpriteRenderer[1].enabled = true;
        } 
        else
        {
            m_SpriteRenderer[1].enabled = false;
        }
    }
}