Just curious if other people see the slightly lighter yellow square in the middle, between the two black pieces. I've got a pretty old monitor, so i don't know if it's starting to go weird or if this is just an optical illusion.

looks like the same yellow to me I even looked hard

I only see a mild illusion of it wanting to complete being a shape within, in other words my eyes want to see black lines on top and bottom of the square. It doesn't look lighter to me. When I rotate it 90 degrees it loses its effect immediately.

Looks fine here.
Here's a fun optical illusion.

I'm a bad person =oD

if you see a darker yellow square in the middle it is your monitor. What you're seeing is likely crosstalk and is often noticeable on poorly designed LCD panels. Almost all panels would be darker there, but to a different degree based on the design. To be sure its not just an optical illusion, you could measure it. If you're on a CRT, i am not sure.

m2h: took me a while to get it + had to switch to internet explorer, i laughed...

same color here.
smoke some weed and it won't matter.*L*

the man speaks the truth

As dough says, either crap design IN the monitor - or crosstalk on an analogue vga connection

It's a CRT, and I'm beginning to notice very faint steaks in places that obviously aren't optical illusion. On a white background, black squares often have a hint of light gray line stretching a few pixels to the right from the top and bottom of the squares. They're not even close to an annoyance yet, so I'm not going to be concerned for now, but I'm guessing this is a result of hardware getting old.

Thanks for the responses, guys.