How to change an object's transparency through Script?

I’m using C# and trying to change the transparency of a UI panel to get a nice red effect on the screen that changes as you lose more health. This is what I have so far:
public Image panel;
public int starting health;
private int health;

    public void Start()
        health = startingHealth;
        panel.color = new Color(130, 0, 0, 0);

    public void TakeDamage()
        health -= 1;
        panel.color = new Color(130, 0, 0, startingHealth - health);

I figured out the problem! So basically the way I was setting it was right it’s just the scale I was setting it at. Instead of the fourth number being between 0 and 255 it’s between 0 and 1. Where 0 is fully transparent and 1 is fully visible.