Flower bulbs and how they work?

Tulips, Daffodils, Hyacinths, Crocus etc... they all come in an array of colors...How are flower bulbs altered in color?

and how do they know when to bloom every year- almost like clock work?

Thxs!

Flower bulbs and how they work?
They are different varieties due to different in DNA color sequence.This is regulated by gene regulation and expression by making novel proteins.
Reply:they must receive a chilling (winter), colors are encoded in the DNA, not the bulb.