Have there always been only 6 color balls in snooker?
The problem with answering this question is that the transition
from Billiard to Snooker is a gradual one - so whilst games existed
with less than six balls it is unclear whether we can call this
snooker.
In its earliest form Snooker was a combination of two Pool type
games - Life Pool and Pyramid Pool. The red balls come from pyramid
pool, and the first colour, the black ball, from life pool. Three
other colours were added a little later, the set being completed
with the introduction of the brown and blue. The inclusion of these
initial colours was first proposed in 1875 - dates for the
inclusion of the brown and blue are unknown. It is unclear how well
received or widespread these initial alterations were, but by 1882
the rules were standardised for a new game known as Snooker, with
all six coloured balls included.
One notable exception to the regular 6 coloured balls is Snooker
Plus, a variation of the six-ball game invented by World
Championship winner Joe Davis. The game introduced an orange ball
(worth eight points) and a purple ball (worth ten points), to make
a total of eight coloured balls, in an attempt to reinvigorate the
game. However, the concept didn't catch on and Snooker Plus is now
widely obsolete