How to assign semitransparency in a shader via Сolor.a

Questions & Answers
1

Shader “Custom/Px1” {
Properties {
_Col (“_ColorAmb”, Color) = (1,1,1,1)
}
SubShader {
Tags { “RenderType”=“Transparent” }

		CGPROGRAM
		#pragma surface surf BlinnPhong alpha
	    
		struct Input 
		{
		float4 color : COLOR;
		};
	
		fixed4 _Col;

		void surf (Input IN, inout SurfaceOutput o) 
		{
			o.Albedo = _Col.rgb;
			o.Alpha = _Col.a;
		}
		ENDCG
	}
}
3

Tags { “RenderType”=“Transparent” }

         CGPROGRAM
         #pragma surface surf BlinnPhong alpha

should be

      Tags { "RenderType"="Transparent" "Queue"="Geometry+1" }
     
             CGPROGRAM
             #pragma surface surf BlinnPhong alpha:auto

That will ensure the queue is correct (can add more if you want further in front) and also that you are alpha testing + blending

2

If your shader is correct, you can assign the color property like this:

material.SetColor("_Col", yourColor);

Where the material is your object material. You can assign it in inspector or get it like this:

var material = theObjectWithTheMaterialYouWantToChange.GetComponent<Renderer>().material;