A Blue cape can be obtained by using Blue dye on a regular black coloured Cape which can be obtained by killing a Highwayman. Dyeing a cape blue (or any other colour) requires a crafting level of 1, and grants the player 2.5 xp in Crafting. A blue cape may also be among the items you can obtain from chasing Solus Dellagar during the Wanted! quest. Additionally, blue capes are sold by Valaine, located in Champions' Guild. The player calls this cape the "Cape of Champions" during the Wanted! quest, as it is sold in the Champions' Guild.
In RuneScape Classic, Blue capes were originally only attainable from the Champions' Guild shop, and were thus worn as a sign of accomplishment. When Dyes came out, they lost popularity as anyone could get one simply by dying their cape blue.
The player may make a reference to blue capes being from the Champions' Guild during the Wanted! quest, if they should receive a blue cape while searching for Solus Dellagar.