In Pokemon Gold and Silver, the ability to have custom made Pokeballs fashioned was introduced. Crystal goes a step further and allows you to have multiple balls crafted at once. After rescuing the Azalea Town Slowpokes, Kurt will reward you with a Quick Ball and the offer to make you more specialty Pokeballs if you bring him Apricorns. Below is a list of what can be made, what Apricorns are needed, and where to find them.

PokéballMade fromEffect
Level Ball Red Apricorn (found on Route 37) Makes catching Pokemon with lower levels than yours easier.
Friend Ball Green Apricorn (found on Route 42) Caught Pokemon are friendlier faster.
Lure Ball Blue Apricorn (found on Route 37) Makes catching Pokemon on fishing line easier.
Moon Ball Yellow Apricorn (found on Route 42) Makes catching Nidoran, Nidorino, Nidorina, Clefairy, and Jigglypuff easier.
Heavy Ball Black Apricorn (found on Route 37) Makes catching heavy Pokemon easier.
Fast Ball White Apricorn (found in Azalea Town) Makes catching Pokemon who can escape battle and the Legendary Dogs easier.
Love Ball Pink Apricorn (found on Route 42) Makes catching Pokemon of the opposite gender to your own easier.