Fenris is right, electrical lines can cause interference. I assume you are running 10baseT, not 100baseT, because 100 is a lot more sensitive to that type of interference. Your post did not mention any problem now. For ease of service now, as well as eliminating interference now and if/when you upgrade to 10/100, or straight 100 gear, those cables should be separated. There have been cases where having even one power line in close proximity to a network cable on a 100bT network has prevented any communication.
One last note, cat5 cable can be a number of colors besides the popular blue that fenris spoke of. Before I came to my current position, they had ran cables in white, blue, black, and 2 shades of gray in addition to the blue. There are many more colors available like red, yellow, green, orange, and purple. They are all sold in bulk reels as well as pre-made patch cords, so you could find any of those colors in an installation.