The soil has to be strongly acidic for blue hydrangeas to be blue. pH needs to be under 5.00 for true clear blue color without purple/mauve hints.

Look at the article in the link, it discusses pH and gives an example of flower color typically found in cultivars like Nikko Blue at various levels on the pH scale.

Here is a link that might be useful: Hydrangea flower color and pH

SG is also pH sensitive. I believe it's supposed to be a rebloomer, so it may not need to be entirely bud-hardy. That said, it might not do so hot in zone 5 for a few years until it becomes more established. However, if your Nikkos do well than this shouldn't disappoint too much. I would pile some leaves over it by December to preserve buds, and leave it like that until after the last frost of Spring.
As it is a picotee/double flowering specimen, it probably doesn't grow quite as large as your others do (look for a good 3-4' by maturity).

As an afternote, I wouldn't worry too much about the exact flower color unless you DEMAND a certain kind, at which point you should amend. BUT I would also amend if your Nikkos for example are experiencing a color so light that the blooms almost look off-white, which is unattractive to me at least.

Horse puckey!! It is the aluminum in the soil that makes blue hydrangeas blue. In less than sufficiently acidic soils, aluminum tends to be unavailable or bound up but you can have a soil pH as low as 4.0 and if there are insufficient levels of aluminum, you will never have a blue flowered hydrangea. Truly, one does not need a soil pH anywhere close to 5.0 to grow blue hydrangeas. Soils in the PNW are typically slightly to moderately acidic.....around 6.0 to 6.5. Due to typical local aluminum concentrations, blue flowered hydrangeas are a uniformly true blue if grown in open organic soil unrelated to any concrete.

I'm not at all sure I'd take the word of the cut flower growing market over those who specialize in growing ONLY hydrangeas :-) FWIW, all colored blossomed macrophyllas are sensitive to pH and aluminum levels to various degrees (whites are unaffected). Some can change fully from blue to pink with soil manipulation but most will only reflect some tonal changes (blues to purplish, pinks to mauve). Intensity of color has to do with variety but not really soil chemistry. One can rarely change the intensity of a color (how strong or pale the color is). The intensity develops for a number of reasons: the heredity of a particular hydrangea variety, weather conditions (hot or cold, humid or dry), health of the plant, and possibly other natural factors. Fertilizing hydrangeas once or twice a year may result in a little more saturated color simply because the health of the plant may be improved.