It has two meanings in the diamond industry.  Usually, it refers to an absence of color—a diamond said to have ‘fine color’ frequently has no visible color at all.  On the other hand, we use the term fancy color to describe naturally colored diamonds with distinct, attractive tints.

GIA Standard
D	Colorless where D being most transparent
E
F
G	Near colorless
H
I
J
K	Faint yellow
L
M
N	Very light yellow
O
P
Q
R
S	Light yellow
T
U
V
W
X
Y
Z
Z+	Fancy color

 Famous Diamonds

Natural Pink Diamonds	Cullinan II, I vs. a 1ct. round	Hope Diamond
Steinmetz Pink, Allnat Diamond De Beers Millennium Star	Tiffany Diamond	Dresden Green Diamond