Default Rainbow Colors Found Using draw_geometries

**Describe the bug**
Although I used pcd.colors to change to the colour I preferred, the built in function draw_geometries doesn't seem to preserve the defined colors.

**To Reproduce**

import numpy as np
import open3d as o3d
from sklearn.cluster import KMeans

**Expected behavior**
specified colour should be pained rather than seeing rainbow

**Screenshots**
after modifying pcd.colors only:

after modifying pcd.points and pcd.colors:

**Environment (please complete the following information):**

- Operating system: Mac Big Sur 11.4
Using python 3.8.10 and 0.13.0 open3d
- Is this remote workstation?
no
- How did you install Open3D?
pip virtual env

**Additional context**
I used Kmeans to cluster points first and would like to filter out some numpy points by specifying coordinates. It is surprised that print(np.asarray(pcd.colors)) gives exactly same output before and after the line--o3d.visualization.draw_geometries([pcd]).