Pointcloud Registration ColoredICP works worse?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

I have three rgbd cameras, and get three pointclouds from different view of cameras. I use ICP registration them, but them work worse. Can you help me?
ICP Paramter voxel_sizes=0..02 iterations=50

pointcloud 1:

pointcloud 2:

pointcloud 3:

before ICP:

after ICP:

And I have another question，three pointclouds merge together and the picture become blurry, How solove it?