I recently made a pair of socks for myself using what looked like a full skein of Madeline Tosh Sock yarn in the Copper Penny colorway that I bought about a year ago. After I finished the first sock, I was pretty sure I didn't have enough to complete the mate so I ordered another skein. Look at the difference in dyelot! I don't mind mis-matched socks, but the difference in dyelots was sure to look like a glaring mistake. So, I started the second sock with the new, darker dyelot, then changed back to the original when I thought I had enough to finish the sock. The color change shouldn't show when I'm wearing long pants.
For those of you interested in the pattern, a very similar pair will be in the July 2011 issue of Sockupied, available from Interweave Press.