Personally, I would utilize black contact paper. Contact paper is relatively cheap and if applied correctly, it will look great and also act as a non-permanent solution. What I mean by this is you can remove it in the future if need be. I’m not sure if this is your first Ball Python or not but if it is, you may very well catch the “Bug” and eventually upgrade to a rack system. If that is the case, you may find another use for your enclosure which would not require three sides to be blacked out. It is always good to keep the future in mind. Even if you don't catch the "Bug" you still might find yourself wanting to reuse the enclosure for something else one day which would make a non-permanent solution the best option.
So, the summary of black contact paper would be:
1. It’s cheap
2. It’s esthetically pleasing
3. It’s non-permanent