The role of phase difference among component holograms in multicolour
holography is described from the hologram fringe contrast point of vie
w. The fraction of the hologram below a certain contrast factor agains
t different phases and hologram types is considered. The holographic t
echniques considered are two- and three-colour holography with irratio
nally related wavelengths, and two-colour holography with frequency-do
ubled lasers.