Soil test time. That's really the only way to know what is going on in your yard.

Lack of soil acidity is not a problem in this part of the country. In spite of some mophead hydrangeas being sold with particular colors attached to their name, the actual colors of the blooms is dependent on several factors. The first is that they need to have an established root system that readily absorb nutrients from the soil. For this reason, you may not see their true color for 2-3 years. I have several Nikko Blue and All Summer's Beauty hydrangeas and their colors were all over the place until they were well established. All of them are now a deep cobalt blue every year. Hydrangea color is also dependent on the amount of aluminum in your soil and the soil pH. A soil test from UMass will tell you what you need to know. As far as the lime, your yard will benefit from lime each year as will a few alkaline loving shrubs such as lilacs. However, most other plants such as roses will tolerate acidic soil as long as it doesn't get too extreme. I've never limed any of my roses and they do just fine.

There ARE some limestone areas in New England, so it depends on your location. And for the most part, in more acidic soils most hydrangeas are more blue than pink, as you surmise. They DO prefer slightly acidic soil, though, so you may compromise the plants' health by adding too much lime if your soil is already neutral.

The cultivars that have been bred for red or pink flowers should do fine in most NE soils, I agree with the other posters that you should wait until they're mature, and get a soil test, before you tinker with the PH.

Old timers here on Cape Cod tell me that adding iron (in the form of old rusty nails and other debris) can deepen the color of most blue hydrangeas. I'm not sure if this has ever been tested, but it gives me a reason to hide all sorts of metal junk under my shrub border.

This is from the National Arboretum FAQ page:

Flower color in H. macrophylla is dependent on cultivar and aluminum availability. Aluminum is necessary to produce the blue pigment for which bigleaf hydrangea is noted. Most garden soils have adequate aluminum, but the aluminum will not be available to the plant if the soil pH is high. For most bigleaf hydrangea cultivars, blue flowers will be produced in acidic soil (pH 5.5 and lower), whereas neutral to alkaline soils (pH 6.5 and higher) will usually produce pink flowers. Between pH 5.5 and pH 6.5, the flowers will be purple (see image at left) or a mixture of blue and pink flowers will be found on the same plant.