Once your Pokeblocks are made you can inspect their qualities. Their colour hints at their flavour more often than not, but you should still check out each individual Pokeblock to make sure it's right for your Pokemon:
Red Pokeblock: Spicy Pokeblock that raises Coolness.
Blue Pokeblock: Dry Pokeblock that raises Beauty.
Pink Pokeblock: Sweet Pokeblock that raises Cuteness.
Green Pokeblock: Bitter Pokeblock that raises Smartness.
Yellow Pokeblock: Sour Pokeblock that raises Toughness.
Purple Pokeblock: Mostly Spicy Pokeblock that raises Coolness and a less dominant contest stat.
Indigo Pokeblock: Mostly Dry Pokeblock that raises Beauty and a less dominant contest stat.
Brown Pokeblock: Mostly Sweet Pokeblock that raises Cuteness and a less dominant contest stat.
Lite Blue Pokeblock: Mostly Bitter Pokeblock that raises Smartness and a less dominant contest stat.
Olive Pokeblock: Mostly Sour Pokeblock that raises Toughness and a less dominant contest stat.
Gold Pokeblock: A high level Pokeblock that raises one or two contest stats.
Gray Pokeblock: A three flavor Pokeblock that raises three three contest stats.
White Pokeblock: A four-flavor Pokeblock that raises four contest stats.
Black Pokeblock: A poor Pokeblock that is created when two or more of the same Berry are blended, or if the Berries force a neutral flavour.
Remember that how effective a Pokeblock is depends on natures, so even if you feed a high quality Pokeblock to your Pokemon it may wind up being a waste if its in its nature to hate that specific flavour. Pokeblocks also have Levels, which is related to the Berries used and how good at blending your berries you are. Blending with more people seems to increase the likelyhood of getting a good level Pokeblock. Finally, the Feel of the Pokeblock also depends on the skill of the people blending, and more importantly how many. The more people blending, the lower the feel. You want to have lower feel Pokeblocks if possible as this means your Pokemon can eat more of them before their sheen is at its maximum and they can eat no more Pokeblocks.