Medium Blue is ten years old. The first LEGO sets including the color were released in 2002 according to information at Peeron.com and since that time some 3,500 elements have been released in this soft, pleasing color, making it currently the 25th most common color for LEGO elements.
Although sometimes categorized as a “girl” color because of its muted tone and inclusion in several Belleville sets, one of the first sets to use medium blue was 4728 Escape from Privet Drive from the Harry Potter series. In that set it was used for the Weasley car, pictured above.
The color has been embraced by LEGO fans, as is evident from a quick Flickr search:
Though not exactly scarce, medium blue elements are not included in large numbers in many sets. They are frequently used to add accent color, as with the recent Imperial Flagship
Some of the current sets that include medium blue elements include Kingdoms Joust and several of the new Friends sets.