These are the colors for the Gildan t-shirts, which have the largest selection.
Note that the colors may not be accurate due to variances in monitor calibration.
ash
Ash
azalea
Azalea
black
Black
blue dusk
Blue Dusk
cardinal
Cardinal
carolina blue
Carolina Blue
cedar
Cedar
charcoal
Charcoal
chestnut
Chestnut
daisy
Daisy
dark chocolate

Dark Chocolate
dark heather
Dark Heather
eggplant
Eggplant
forest green
Forest Green
gold
Gold
heather cardinal
Heather Cardinal
heather indigo
Heather Indigo
heliconia
Heliconia
ice grey
Ice Grey
indigo blue
Indigo Blue
iris
Iris
irish green
Irish Green
jade dome
Jade Dome
kelly green
Kelly Green
key lime
Key Lime
leaf
Leaf
light blue
Light Blue
light pink
Light Pink
maroon
Maroon
metro blue
Metro Blue
military green
Military Green
navy
Navy
oceana
Oceana
olive
Olive
orange
Orange
pine
Pine
pistachio
Pistachio
prairie dust
Prairie Dust
purple
Purple
red
Red
royal
Royal
sand
Sand
sapphire
Sapphire
serene green
Serene Green
sport grey
Sport Grey
steel
Steel
stone blue
Stone Blue
tan
Tan
tangerine
Tangerine
texas orange
Texas Orange
uniform navy
Uniform Navy
vegas gold
Vegas Gold
violet
Violet
white
White
yellow haze
Yellow Haze