It's a single color, but is thousands of pixels on a side. In GIF form it compresses down to only a few kilobytes, but when your computer tries to uncompress it for display it balloons out to a whole bunch of megabytes. At the very least your system will take a long time to do the uncompression and display, during which time it will be unresponsive. Most likely your browser will run out of memory and fail to display the GIF, possibly exitting.
Some people report that their computer actually reboots.
By the way, I had to write a custom program to produce a GIF this big. The standard GIF writers crapped out on sizes that could still be displayed. Back to Killer Web Pages .