Captured at an angle, two adjacent doors appear to tilt, thrusting themselves into our line of vision. Suffused with a soft glow, they compete to entice viewers into alternative, equally mysterious, realms. This is Blue Book #2, one of thirty-six untitled images in “Blue Book,” 2009, Dayanita Singh’s series of photographs of industrial sites and deserted, down-at-the-heel interiors swaddled in shades of . . . you guessed it: blue. The deep indigo of corrugated rooftops in Blue Book #9, for example, vies for attention with the wide expanse of azure sky (punctuated with a teardrop-size white moon)