Shader light - Problem

Hi, I'm using this code to create a customizable shirt color with a print, and i'm trying to add the scene light to the shader, when I activate the light using a tag the print on the shirt disappear, how do I make both works?

 // Upgrade NOTE: replaced 'SeperateSpecular' with 'SeparateSpecular'
 
 Shader "ShaderAvatar/TShirt" {
     Properties {
         _MainTex ("Color Base", 2D) = "white" {}
         _DetailTex ("Details", 2D) = "white" {}
         _Color ("Main Color", Color) = (1,1,1,1)
 
     }
 
     
     SubShader {
              //Tags { "LightMode" = "ForwardAdd" } 
 
        Pass {
 
             SetTexture [_MainTex] {
                 constantColor[_Color]
                 combine constant lerp(texture) previous
             }
             SetTexture [_DetailTex] {
                 combine texture lerp (texture) previous 
 
             }
 
         }       
     }
 } 

 using UnityEngine;
 using System.Collections;
 
 public class example : MonoBehaviour {
     
     private Color c;
 
     
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         GameObject.Find("polySurface1").renderer.material.SetColor("_Color",new Color((c.r/255),(c.g/255),(c.b/255),1));
     }
     
     void OnGUI(){
         
         GUI.color=c;
         GUILayout.Label("Así o más largo");
         GUI.color=Color.red;
         c.r=GUILayout.HorizontalSlider(c.r,0,255);
         GUI.color=Color.green;
         c.g=GUILayout.HorizontalSlider(c.g,0,255);
         GUI.color=Color.blue;
         c.b=GUILayout.HorizontalSlider(c.b,0,255);
         GUI.color=Color.white;
         
 
             
     }
 }