Your code can be fixed as follows:

import numpy as np, cv
vis = np.zeros((384, 836), np.float32)
h,w = vis.shape
vis2 = cv.CreateMat(h, w, cv.CV_32FC3)
vis0 = cv.fromarray(vis)
cv.CvtColor(vis0, vis2, cv.CV_GRAY2BGR)

Short explanation:

1. np.uint32 data type is not supported by OpenCV (it supports uint8, int8, uint16, int16, int32, float32, float64)
2. cv.CvtColor can't handle numpy arrays so both arguments has to be converted to OpenCV type. cv.fromarray do this conversion.
3. Both arguments of cv.CvtColor must have the same depth. So I've changed source type to 32bit float to match the ddestination.

Also I recommend you use newer version of OpenCV python API because it uses numpy arrays as primary data type:

import numpy as np, cv2
vis = np.zeros((384, 836), np.float32)
vis2 = cv2.cvtColor(vis, cv2.COLOR_GRAY2BGR)

There is nothing wrong with installing common dependencies using your operating system's package manager, remember using pip means your synaptic updates won't update your Python libraries and pip won't leverage the dependencies already taken care of by aptitude. For python packages with C extensions like numpy and opencv its probably better to use apt-get.

In Ubuntu you can install both dependencies with

sudo apt-get install python-numpy python-opencv

The actual Python error you are getting indicates what is wrong, namely that you are executing from within the numpy source directory, or have a file named numpy.py in your current directory which is confusing things at import time. Try change into an empty directory, start Python import your libraries:

import numpy
import cv

Hope that helps.