material.SetTexture reset

I'm working on a project (I've finished my "Hide and Seek" one) and am working on a fighting game like smash bros. i have gotten the character (For now a goku sprite) and have gotten it to look one way when moving, and the other, but when the key is released. they stay the way they are. if i use

 if(Input.GetKeyUp(KeyCode.Key))

it makes a grey box covering my character.

My current script:

 using UnityEngine;
 using System.Collections;
 
 public class GokuAnimate : MonoBehaviour {
     
     public Texture gokuMove;
     public Texture gokuMoveL;
     public Texture gokuStand;
     
     void Update () {
         if(Input.GetKeyDown(KeyCode.D))
         {
             renderer.material.SetTexture("_MainTex", gokuMove);
         }
         
         if(Input.GetKeyDown(KeyCode.A))
         {
             renderer.material.SetTexture("_MainTex", gokuMoveL);
         }
         
     }
 }