On this 1910 picture postcard, the black was printed with a halftone process, the image being broken into dots by a screen. The colors were applied as washes, possibly stencils, with no effort to be especially realistic.
St. John's Lake is now called Lake Sagatagan. The grandly-named "Bridge of Sighs" was on the trail along the shoreline to Stella Maris Chapel. The footbridge was near the present-day Prep School practice fields, where there is now a covered bridge.
For more information on St. John's "Bridge of Sighs," see:
Roske, Peggy, Lake Sagatagan's Pickerel Point Bridges, 2014.