Grape hyacinths normally grow foliage in the fall - freezing temperatures don't bother them and what they really seek to avoid by going dormant is the summer's heat; they are active throughout fall, most of winter and spring.

Your showy hyacinths do not normally have leaves this time of year, but underground they (and most other bulbs) are growing shoots that are working their way towards the surface. The growth is pretty slow and will continue until the shoots breach the surface in spring, and break open into leaves.

The bulbs may be planted too shallow in the pots, causing the leaves to appear a few months early.

Because they are in containers, though, an additional problem is that they are more prone to temperature fluctuations and will be warmer every mid-day throughout winter than they should be if they were in the ground. The sides of the pot capture quite a bit of sunlight coming at a slant from the South this time of year - and so South-facing surfaces get much more sun than the ground does. If they are near the southerly wall of a home, garage or deck, that will generate additional warmth (from sunlight) so the bulbs don't "realize" it's winter.

I think your hyacinths will be fine - but what you ought to do put an inch or two of extra soil, plus leaves and mulch, in the pots to cover the leaves. That will bury the bulbs so they are deeper and have farther to grow before breaching the surface, but it also insulates them from the spike of warmth occurring each day from sunlight.

You should also move the pots to the shade so they'll cool off more. You may even want to set them in a spot where they will be covered by snow drifts. That will ensure that they do indeed go on "pause" during the cold months and stay at a consistent temperature, but since snow is a good insulator it will protect the already-exposed shoots from the coldest frosts.

For the most part hyacinths can handle frigid cold, because they routinely do all their growth and even blooming before the average last frost date, so are regularly exposed to sub-freezing temperatures even when they are most active. I think the leaves will be fine, but in order to prevent the flowers from emerging in winter you need to keep them cool with shade and mulch.

Thank you, pizzuti, for that comprehensive answer.