I think hydrangea bloom color is determined by the soil pH. The reason most of them in SK are pink is because of the alkaline soil through most of the province, if I had to guess. I think they bloom blue in a very acid soil (4.5, if I remember correctly), so if you can and are willing to amend your soil to that, they should bloom blue for you . . . that would probably be quite a task, though. I only know this because I also am not that fond of pink, but I am not willing to even try to change my pH by that much. The hardiness should be the same, regardless of the bloom color, since the same plant can bloom pink, white, or blue, depending on pH.

When I was down in Louisiana many years ago I was told that they get the shading of color from blue to pink by the number of nails they stick in the ground around the plant. I can not remember which way the color went, but the gardeners kept buckets of nails in water to pre rust them before sticking them in the ground, it did take a lot and they added every year. I think the nails turned the plants pink. I also think that the trick only worked with older varieties, the newer ones are bred to breed the color true. Don' think this helps you much but maybe

The nails will rust and acidify your soil. Then they should turn the blue color. I think it would take alot though.
BTW, I have put pieces of steel by my Blue Spruce to turn them more blue. It works.

I only have one Hydrangea. Pinky Winky...you can tell by the name what color it is.
Shelley

Does that mean that my very outdated gardening books are . . . outdated? And that there are hydrangeas now that come in a stable color regardless of soil pH?

Yes. Hydrangea macrophylla are the ones with pH sensitive flowerhead colours. Hydrangea paniculata have stable flowerhead colour. 'Pinky Winky', 'Limelight' are a couple of examples.

So, in theory at least, if I planted hydrangea near evergreens, which also like acidic soil, I could feed them my coffee grounds and some rusty metal and maybe get a shade of blue?

Maybe. You could also get some aluminum sulphate and try that.