Found at The Shark Tank (Computerworld)
http://blogs.computerworld.com/16322/aha?source=CTWNLE_nlt_shark_2010-06-15
This tech goes on vacation -- something his co-workers dread, reports another technician on the scene.
"Problems always arise when he leaves," a co-worker says. "And so it happened: We have a computer gathering data on all outgoing phone calls in our company. The operator noticed that there were no new records that week, and called us.
"We went to the room where the computer stood amidst a jungle of cables, without knowing what their use was.
"After a half-hour of fighting with it, we had to disturb our friend on his vacation. Luckily he answered and told us that the solution was simple: We just had to plug the dark gray cable to the computer.
"We took a look, but found no 'dark' one, but simply a bunch of equally gray cables.
"After scratching our heads and telling him that we could not find it, we noticed a lonely red cable. We plugged it in and voila! Everything was back to normal.
"That's when we remembered that he was color blind."