In brief: few people would have wanted or needed such images, and they were expensive to make.

Although color photography was widely available by the mid 1950s, few publications printed photos in color. Local newspapers and church publications almost never had the budget for color printing. Since SUCH publications often developed their own photographs, the chemistry and processing were vastly simpler if they stuck to black and white.

Only the glossiest national publications—Life, Look, National Geographic—printed color inside, though many magazines used color on their covers. It might seem you could shoot color film for both purposes, but the conversion to grayscale gave inferior results prior to the Photoshop era. As a magazine photographer in the 1980s, I typically carried two camera bodies, one loaded with black-and-white film and one with color slide film.

Commercial photographers, which church leaders might have hired to photograph their buildings or programs, also stuck with black and white for a long time, both for reasons of cost and because they also typically did their own processing and printing. Color slide film was notoriously finicky about precise exposures, while color print films of the era often faded or color-shifted (from fading of certain color dyes) within a few years. Large prints, of the size that the diocesan office might hang on the wall, were quite expensive to have printed prior to the digital era.

Color photography in the 1950s was dominated by color slides, and most were taken by travel enthusiasts, railfans, or architecture buffs. They typically would have had no reason to photograph these sites or buildings. By the 1970s, color snapshots were common for family pictures, but those would typically have been images of family members, not the facility. Even then, black-and-white snapshots were less expensive to shoot and have printed, and the cost differential may well have been even larger in Canada.

The digital revolution changed this landscape dramatically in the 1990s, first by making it much easier to print color images (either single prints or as part of a publication) and then by making the images themselves digital, from capture through manipulation to display.

The pictures you're thinking of were, for the most part, taken by the National Film Board, which had a photography division that was started in 1941 (or rather, "acquired" -- it took on the Government Motion Picture Bureau which had a photography group).

The vast majority of the NFB's pictures were in black and white all the way up to the mid-1960s. This is for a couple reasons:

a) They considered their mission of documenting Canada to be a journalistic one, and their pictures would be printed in regional newspapers and magazines. The NFB didn't publish their own books until starting in the 1960s; these photo books enabled the use of color.

b) There was a general impression in the 1950s especially (when the majority of the photos in question were taken) that there strong aesthetic purpose to black and white photography as "serious", and color belonged more to "pop culture". The famous NFB photographer Ted Grant once said:

If you photograph people in black and white you photograph their souls, but if you photograph them in colour you photograph their clothes.

which gets the general attitude at the time. Additionally, the vast portfolio of pictures tried to have an internal consistency to them (both for journalistic and artistic reasons), so consistency with the entire collection being of a similar black-and-white style was an intentional choice.

c) Color photography was more expensive. Chris Lund, another NFB photographer, is quoted as saying:

We’d keep colour for when a very colourful, interesting shot could be made easily. Processing of this was very costly at the time. Then there was the user - Who’s going to use it? It was expensive for photo engraving. So we stuck to black and white.

In other words, even though they were perfectly capable of taking a color shot, actually printing in color was far more expensive than magazines generally wanted to pay.

...

Freund, A. & Thomson, A., Eds. (2011). Oral History and Photography. New York: Palgrave Macmillan.

Payne, C. (2013). The Official Picture: The National Film Board of Canada's Still Photography Division and the Image of Canada, 1941-1971. Canada: McGill-Queen's University Press.

As a newspaper person I recognise and agree with everything MrDowntown says below, and I have no reason to doubt jbdyer.

Nevertheless, why is no-one making it clear in what period Canadian residential schools existed?

My guess would be that Canadian Residential Schools represented not residential schools in general but a specific class or category, perhaps official.

Why is leaving that up to Members' prior knowledge a good idea?