Blue shadow on monitor
 

This is probably just a weird hardware problem, but I didn't know where else to ask, so here it is.

I have a 4PC KVM switch allowing my 2 laptops and Lubuntu desktop to share a monitor and keyboard/mouse.
Sharing works but the monitor gets a weird blue shadow when I switch to the desktop and one of the Windows laptops. On two other laptops, the display works fine.
I tried everything I can think of. Switching cables, connecting the monitor directly to each machine, etc. The one windows laptop consistently has the blue shadow, the Lubuntu desktop has it when the KVM is used, and seems to sometimes have it when connected directly. The weird part is I've used the monitor for months on that Lubuntu desktop with no problems what so ever.
I even switched the monitors, but still the problem remains the same. I'm guessing some sort of weird interference - the cables look cheap and there is parallel USB cable that's semi-attached to the monitor cable.
Switching the cables does not seem to solve the problem, neither does switching the ports on the KVM switch.

Any ideas?

Check to make sure all of the equipment is plugged into a common 3-wire AC circuit so they share the same short ground connection. I've seen that kind of problem from poorly grounded stuff. Also, if the monitors are too close together they can interfere, but that usually shows up as a wiggle rather than a shadow.

I think I narrowed it down to bad wires. 2 of the 4 were doing it, swapping them with the other 2 solved the problem it seems. I guess I was swapping with a bad wire which was confusing the problem.

I had the same problem when I put a radio spaker (unshielded of course) close to my monitor. Moving the speaker away solved the problem of blueish, redish and greenish cast from the monitor. Colors were changing depending of how the speaker is turned to the monitor. Bad cables can do the same thing.