Look at the image below before taking the link:
Without looking at the write-up, just off the top of your head what colors are the rectangles in that image, and what are the relative pixel-widths of the lines?
Are the two gray rectangles really gray? Are they wider than the black rectangle? Are they the same width as the red rectangle?
In a running discussion on the
MSDN Silverlight Forum, Michael Schwarz, Luis Abreu, and this author had a discussion about just this circumstance.
You may be surprised at the answers!