Myriad shades of blue wash over the walls of Chefchaouen, a remote village cradled in the rugged Rif Mountains of northeastern Morocco.     Nicknamed Morocco’s “Blue City,” the town is one of the dreamiest places in this North African country. Smaller and calmer than frenzied Fez and Marrakesh, Chefchaouen’s arched doorways and maze-like alleys create stunningly blue photo backdrops.     In the heat of summer, tourists snapping selfies can overrun the medina, or old city. However, when I added a winter weekend in Morocco’s...