Not so long ago, cauliflower was about the most boring looking vegetable on the planet, coming in beige and only in beige. Today, cauliflower is a riot of color.
At farmers markets right now you can find it in a lovely shade of orange (a variety called "Cheddar") and even lavender (called "Graffiti"). If that's not enough, you can always check out our old friend romanesco, with its tightly shaped pale green cones (this is called a broccoli, but genetically it is a cauliflower variety).
The good thing about all of this color is, unlike with many vegetables, it lasts through cooking -- particularly if you add a little acidity, either vinegar or lemon juice.
Cauliflower heads should be firm and tightly closed. White varieties should be very pale, with no dark "sunburned" spots. Reject any heads that show signs of softness, that's the start of spoilage.
Though it seems durable, cauliflower is extremely perishable. Keep it tightly wrapped in the crisper drawer of the refrigerator.