Pythonでopenpyxlを使用してExcelファイルを生成することができますが、グラフに設定できるカラーとして以下があります。
openpyxl.drawing.colors module
しかし、名前を見ても実際のカラーが分からなかったので実際に全てのカラーを設定したグラフを生成しました。
mediumTurquoise
wheat
royalBlue
ltGrey
darkSlateBlue
dkSlateBlue
deepPink
oliveDrab
violet
honeydew
brown
dkOrange
slateGrey
tomato
indigo
khaki
ltSlateGray
azure
mediumOrchid
lightGoldenrodYellow
lightSkyBlue
dkMagenta
lightSlateGrey
ltYellow
mediumSeaGreen
darkGray
dkTurquoise
moccasin
paleVioletRed
purple
slateBlue
dodgerBlue
seaShell
darkOliveGreen
dkOliveGreen
lightSteelBlue
ltGoldenrodYellow
medTurquoise
snow
teal
aliceBlue
dkCyan
lawnGreen
lightPink
aquamarine
dkOrchid
aqua
ltSteelBlue
sienna
blueViolet
mintCream
cornsilk
mistyRose
burlyWood
mediumVioletRed
seaGreen
darkKhaki
powderBlue
dkBlue
antiqueWhite
darkOrchid
floralWhite
darkMagenta
hotPink
darkCyan
darkSlateGrey
cadetBlue
dkRed
greenYellow
medSeaGreen
skyBlue
lightSalmon
medOrchid
mediumAquamarine
chartreuse
dkSlateGrey
linen
medVioletRed
yellowGreen
ltCyan
magenta
darkSlateGray
deepSkyBlue
grey
olive
lightGrey
lemonChiffon
lightBlue
midnightBlue
mediumSpringGreen
lavenderBlush
lightYellow
dkGrey
blanchedAlmond
crimson
oldLace
navy
bisque
cornflowerBlue
dimGrey
ltSlateGrey
ltSalmon
limeGreen
plum
slateGray
white
rosyBrown
ltBlue
lime
gray
salmon
darkSeaGreen
dkGreen
ltSkyBlue
orchid
ltSeaGreen
beige
forestGreen
peru
blue
ltCoral
darkOrange
medPurple
darkTurquoise
darkGoldenrod
whiteSmoke
goldenrod
ltGreen
navajoWhite
orange
gold
green
saddleBrown
lightGray
medSpringGreen
lightSeaGreen
papayaWhip
fuchsia
dimGray
darkGrey
mediumSlateBlue
darkViolet
dkViolet
ltPink
medAquamarine
dkSalmon
maroon
lightCoral
dkSlateGray
coral
lightSlateGray
medSlateBlue
indianRed
darkBlue
ivory
medBlue
dkGoldenrod
paleGreen
thistle
dkGray
firebrick
pink
ghostWhite
lavender
tan
mediumPurple
red
springGreen
steelBlue
sandyBrown
dkKhaki
lightGreen
paleGoldenrod
darkRed
lightCyan
darkSalmon
black
chocolate
ltGray
peachPuff
silver
turquoise
yellow
dkSeaGreen
orangeRed
paleTurquoise
cyan
gainsboro
darkGreen
mediumBlue