How to apply two colors to the object?

At first I can imagine 2 simple answers:

• If you're using Unity's cube, put 2 of them side by side and change their colors individually

• By using any modeling program, it's kinda easy to assign 2 materials to the same model, either by creating a few more vertices and changing their face materials, or by UV Mapping, which would probably lead you to work with "Texture mapping", not necessarily with real texture, just colors.

You can use the Mesh class to change the cube mesh' vertex colors, and use a shader that supports vertex colors with it. This will automatically give you a smooth gradient between vertices of different color. To find out which vertices are where on the cube, you have to either use the trial and error approach, or use a simple function that displays the vertex number closest to the mouse cursor, like this one I wrote:

 public void GetVertexIndices() {
         Ray mouseRay = Camera.main.ScreenPointToRay (Input.mousePosition);
         RaycastHit hit;
         
         if(Physics.Raycast(mouseRay, out hit, Mathf.Infinity) == true) {
 
             if(hit.collider.gameObject.GetComponent<MeshFilter>() == null) {
                 Debug.Log("Hit object has no MeshFilter!");
                 return;
             }
 
             Mesh mesh = hit.collider.gameObject.GetComponent<MeshFilter>().mesh;
 
             Vector3[] vertices = mesh.vertices;
             int[] triangles = mesh.triangles;
             int vertexIndex0 = triangles[hit.triangleIndex * 3 + 0];
             int vertexIndex1 = triangles[hit.triangleIndex * 3 + 1];
             int vertexIndex2 = triangles[hit.triangleIndex * 3 + 2];
             Debug.Log("Indices for triangleIndex " + hit.triangleIndex + ": " + vertexIndex0 + "," + vertexIndex1 + "," + vertexIndex2);
             //Debug.Log("Vertex Positions: " + vertices[vertexIndex0] + "," + vertices[vertexIndex1] + "," + vertices[vertexIndex2]);
         }
     }