# Unity Vertex Color Shader with Transparency

I'm trying to achieve a simple effect: I have a cube mesh and I want some of the vertices to change color. In this case, I want it to form some sort of a gradient where the unchanged vertices are set to the default color (with alpha = 1) and the changed vertices to slowly fade (default color with alpha decreasing towards 0).

I'm able to modify these vertices' color with this piece of code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
Mesh mesh;
Vector3[] vertices;
Color[] colors;
List<int> verticesToChange;

void Start()
{
mesh = GetComponent<MeshFilter>().mesh;
vertices = mesh.vertices;
colors = new Color[vertices.Length];
verticesToChange = new List<int>();

for(int i = 0; i < vertices.Length; i++) {
colors[i] = Color.white; //Set the default vertex color
if(Mathf.Approximately(vertices[i].y, 0.5f)) //Change only the vertices on the plane y=0.5
}

}

void Update()
{
foreach(int i in verticesToChange) {
colors[i].a = Mathf.Max(colors[i].a - Time.deltaTime * 0.5f, 0f);
}

mesh.colors = colors;
//Not needed here, but I will be changing the vertices' position too later
mesh.RecalculateBounds();
mesh.RecalculateNormals();
mesh.RecalculateTangents();
}
}


My problem is selecting a shader that actually uses this color and this color only. I've tried Unlit/Color, Unlit/Transparent and Particles/Standard Unlit with multiple combinations of Rendering Mode, Color Mode and Albedo color.

Is there a built-in shader that does this and I'm not getting the right combination of its parameters? Or do I have to build my own shader? I've never wrote a shader with Unity, so I would prefer a built-in option or an open source / free shader.