Runtime vertex color painter

gistfile1.cs

using UnityEngine;
using System.Collections;

public class VPainter : MonoBehaviour
{
	public MeshCollider[] paintTargets = new MeshCollider[0];
	
	public Color targetColor;
	public float paintRadius = 1f;
	public float paintSpeed = 1f;
	
	public void Update ()
	{
	
	    if(Input.GetKey(KeyCode.Mouse0))
	    {
	        Ray r = Camera.main.ScreenPointToRay(Input.mousePosition);
	
	        foreach(MeshCollider target in paintTargets)
	        {
	
	            RaycastHit hit;
	
	            if(target.Raycast(r, out hit, Mathf.Infinity))
	            {
	
	                var mesh = target.sharedMesh;
	
	                var colors = mesh.colors;
	
	                var vertices = mesh.vertices;
	
	                if(colors.Length != vertices.Length)
					{
	                    colors = new Color[vertices.Length];
					}	 
	
	                //Loop through the vertices of the mesh to see which ones we hit
	                for(int i = 0; i < vertices.Length; i++)
	                {
	                    //Convert the vertex into world space
	                    var point = target.transform.TransformPoint(vertices[i]);
	
	                    float distance = Vector3.Distance(point, hit.point);
	
	                    //If the vertex is too far away, don't perform any calculations
	                    if(paintRadius < distance) continue;
	
	                    float factor = 1-distance/paintRadius;
	
	                    colors[i] = Color.Lerp(colors[i], targetColor, paintSpeed * factor * Time.deltaTime);
	                }
	
	                mesh.colors = colors;
	            }
	        }
	    }
	}
}