Hyacinths are like hydrangeas in that the color of the petals can change depending on the acidity of the soil. In acid soil with a lower pH the blooms will be blue. Even if you plant blue hyacinths,  after a few seasons the roots may grow into your own more alkaline soil and turn pink. White varieties stay white. If you want to keep your hyacinths (or your hydrangeas) blue you can add aluminum sulfate to the soil to make it more acid. Look for this product with the label "Garden Select" and you will be getting the form in a polymer coated granule just like Osmocote plant food. Just work the granules into the soil a bit, water and by next spring you should see more blue than pink hyacinth blooms. Plants are pretty amazing and changing the color of the blooms is a fun way to experiment in your garden. Keep growing, Marianne Binetti