alpha adjustable additive blender

Hello my game is 2D game using planes with fixed z-coord
in Effects, i often using Additive Blender. (Blend one one)
but i need an additional functions : alpha-adjustable additive blender.

for EX, in code)

 render.material.SetColor("_Color", new Color(1,1,1, new_alpha));

 

render.material.SetColor("_Color", new Color(1,1,1, new_alpha));

but i don't know any shader language and i don't know how to use unity shader.

i tried many thing.

the next is origianl code for additive is next: (and also i using it's other versions...)

 Properties {
 _MainTex ("Base (RGB)", 2D) = "white" {}
 }
 Category 
 {
     ZWrite Off
     SubShader {
         Tags { "Queue"="Transparent" }
     
         pass{
         
             // Blend SrcAlpha OneMinusSrcAlpha //AlphaBlend
             Blend One One//Additive
             // Blend One OneMinusDstColor//Soft Additive
             // Blend DstColor Zero//Multiplicative
             //Blend DstColor SrcColor//2X Multiplicative
             
             
             Material{
                 Diffuse[_Color]
             }
             
             SetTexture[_MainTex] {
                 combine texture
             }
         }//pass
     }//subshader
 }//category

---

and i change it to next (for alpha adjustable)

---

 Properties
 {
     _Color ("Main Color (A=Opacity)", Color) = (1,1,1,1)
     _MainTex ("Base (RGB), Alpha (A)", 2D) = "white" {}
 }
 Category 
 {
     ZWrite Off
     SubShader {
         Tags { "Queue"="Transparent" }
     
         pass{
         
             // Blend SrcAlpha OneMinusSrcAlpha //AlphaBlend
             Blend One One//Additive
             // Blend One OneMinusDstColor//Soft Additive
             // Blend DstColor Zero//Multiplicative
             //Blend DstColor SrcColor//2X Multiplicative
             
             
             Material{
                 Diffuse[_Color]
             }
             
             SetTexture[_MainTex] {
                 constantColor [_Color]
                 combine texture, constant
             }
         }//pass
     }//subshader
 }//category

---

but the alpha isn't work.
i don't know why this problem happen.

please help me~!