Sanco offers pond dye in liquid and dry pack form. In terms of effectively coloring your pond there is no benefit to using one over the other. The most evident difference is the cost increase from liquid to dry pack.
Sanco has three different colors of pond dye:
Crystal Blue and Black Out are offered in both liquid and dry pack form, the Ocean Blue is only offered in liquid. One gallon of liquid pond dye treats the same as one box of dry pond dye. However, the cost of the dry packs is higher. The reason behind this comes down to convenience and packaging. The dry packs are very convenient; you simply open the box and toss the packs in, no spillage to worry about. The packaging is more expensive because of the water soluble bags opposed to the simple gallon jug.