Quad vertex color shader

I need a shader that paints the 4 vertexs of a quad, with customizable colors. I already have this shader, which paints vertexs 2 and 2, with a gradient between them (required too in the 4 different vertex color). I have been wondering and have no clue how to make this 2-2 vertex color to 4 vertex colors.

 Shader "Custom/GradientWhiteToAlpha" {
     Properties{
         //_MainTex("Color (RGB) Alpha (A)", 2D) = "white" {}
         _ColorTop("Top Color", Color) = (1,1,1,1)
         _ColorBot("Bot Color", Color) = (1,1,1,0)
     }
 
     SubShader{
         Tags{ "Queue" = "Transparent" "RenderType" = "Transparent" }
         LOD 100
 
         ZWrite Off
         Blend SrcAlpha OneMinusSrcAlpha
 
         Pass{
             CGPROGRAM
 
             #pragma vertex vert 
             #pragma fragment frag
             #include "UnityCG.cginc"
 
             fixed4 _ColorTop;
             fixed4 _ColorBot;
 
             struct v2f {
                 float4 pos : SV_POSITION;
                 float4 texcoord : TEXCOORD0;
             };
 
             v2f vert(appdata_full v) {
                 v2f o;
                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                 o.texcoord = v.texcoord;
                 return o;
             }
 
             fixed4 frag(v2f i) : COLOR{
                 fixed4 c = lerp(_ColorTop, _ColorBot, i.texcoord.y) * step(0, i.texcoord.y);
                 return c;
             }
 
             ENDCG
         }
     }
 }

^ This shader result is like this:

The one I'm asking for help would be like this:

Thanks!