converting JS to C# for Alpha channels and animation

I am trying to convert this JS to C#.
this is my JS that i made

#pragma strict

var whateverglow : UnityEngine.Animator;
var hashthingglow : int = Animator.StringToHash("StartGlow");
var logovis : float;

function Start () {
 whateverglow = GetComponent("Animator");
}

function Update () {
	GetComponent(SpriteRenderer).color.a = logovis; //change logovis variable between 0-1 to tell how clear it is.
   whateverglow.SetTrigger (hashthingglow);
}

And this is what I have converted it to but there seems to be a error in line 18 (I’m not too familiar with C#)

using UnityEngine;
using System.Collections;


public class logoclass : MonoBehaviour {


	UnityEngine.Animator whateverglow;
	int hashthingglow = Animator.StringToHash("StartGlow");
	float logovis;


	void  Start (){
		whateverglow = GetComponent<Animator>();
	}

	void  Update (){
		GetComponent<SpriteRenderer>().color.a = logovis; //this doesn't seem right.
		whateverglow.SetTrigger (hashthingglow);
	}
}

The error i get is: C:\Users\Owner\Google Drive\Game\Game\Assets\GameScripts\NewBehaviourScript.cs(3,3): Error CS1612: Cannot modify the return value of ‘UnityEngine.SpriteRenderer.color’ because it is not a variable (CS1612) (Assembly-CSharp)

@AAcat

Try this

using UnityEngine;
using System;


public class LogoClass:MonoBehaviour
{
    
    public Animator whateverglow;
    public int hashthingglow = Animator.StringToHash("StartGlow");
    public float logovis;
    
    public void Start()
    {
        whateverglow = GetComponent<Animator>();
    }
    
    public void Update()
    {
        var tmp_cs1 = GetComponent<SpriteRenderer>().color;
        tmp_cs1.a = logovis;
        GetComponent<SpriteRenderer>().color = tmp_cs1; //change logovis variable between 0-1 to tell how clear it is.
        whateverglow.SetTrigger (hashthingglow);
    }
}