Because of the way asphalt spreading was performed in 1931, those particular boots had the knee length and "extra" sole (which was heavily weighted) added to provide the worker spreading the asphalt with more stability; the extra sole was not added for height, though it did help to increase The Monster's stature. They were chosen for
Frankenstein because they were considerably larger than normal boots of the day and, like the shortened coat sleeves, would give the impression of enlarged extremities, and the extra weight would contribute to The Monster's lumbering gait. Because the added weight (approximately 13 lbs. for each boot) aggravated Karloff's bad back, custom-made (and lighter) boots were used for
Bride of Frankenstein and
Son of Frankenstein.
Modern asphalt spreading is largely done by machine, so this type of boot hasn't been used for decades. There is a modern version of asphalt spreader boots available, but they look like a regular workboot; specially treated leather and soles are used for heat-resistance and to provide the wearer with a layer of insulation as protection from the heat, but the added weight is no longer necessary.
I don't recall ever reading anything that confirmed the actual color of The Monster's wardrobe; it could easily have been any dark color. For black and white photography, designers would use whatever color photographed correctly for their purposes. The Monster's "green" fleshtone, for example, is derived from the makeup Jack Pierce used--variously described as "blue green", "gray green", and "yellow green", Pierce chose this color so that it would photograph as pale flesh to give The Monster a "death pallor". Chocolate syrup was often used for blood. And "home movie" footage shot behind the scenes on the set of
Son of Frankenstein revealed The Monster's shirt and sheepskin tunic to actually be reddish-brown in color:
For the 1931 version, I would stick with basic black for the shirt, coat, pants, and boots, as this is the color most people associate with The Monster's clothing. And, IIRC, they used wool for the coat and pants.
I hope this information helps!
