How to affect Shader _Color by the Tint Color of Button (Through Shader)

Hi All,

I would like to ask, how to rewrite following simple luminance shader, to be able to affect its _Color by component tint color, eg. by button tint (image color and transition states colors) etc. The answer should be - the same way how eg. the builtin GUI/Text Shader does, but with that luminance effect. But I can not figure it out.

I would like to use that shader for UI grayscale sprites and make it to work with color tint transitions of button.

Here is the difference between 1. classic tint - 2. luminance tint - 3. only texture

And here is the luminance shader:

 Shader "Custom/Luminosity"
 {
     Properties
     {
         _Color("Tint", Color) = (0.5, 0.5, 0.5, 1.0)
     }
 
     SubShader
     {
         Tags
         {
             "Queue" = "Transparent"
         }
 
         ZWrite Off
         Blend SrcAlpha OneMinusSrcAlpha
 
         Pass
         {
             SetTexture[_MainTex]
             {
                 constantColor[_Color]
                 combine texture * constant quad, texture * constant
             }
         }
     }
 }