En CSS la propiedad background-color se utiliza para dar un color de fondo a un elemento HTML
.elemento{ background-color: #000;}
En el ejemplo anterior he utilizado un color hexstar, pero podría haber utilizado un color rgbstar o hslstar o incluso colores con transparencias como rgbastar o hslastar.
.rgb{ background-color: rgb(0,0,0);}
.rgba{ background-color: rgba(250,100,0,.5);}
.hsl{ background-color: hsl(0,100%,50%);}
.hsla{ background-color: hsla(180,100%,50%,.8);}
También podría haber utilizado nombres de colores como por ejemplo black.
NombreHexRGBhslColor
AliceBlue#F0F8FFrgb (240,248,255)hsl(208,100%,97%) 
AntiqueWhite#FAEBD7rgb (250,235,215)hsl(34,78%,91%) 
Aqua#00FFFFrgb (0,255,255)hsl(180,100%,50%) 
Aquamarine#7FFFD4rgb (127,255,212)hsl(160,100%,75%) 
Azure#F0FFFFrgb (240,255,255)hsl(180,100%,97%) 
Beige#F5F5DCrgb (245,245,220)hsl(60,56%,91%) 
Bisque#FFE4C4rgb (255,228,196)hsl(33,100%,88%) 
Black#000000rgb (0,0,0)hsl(0,0%,0%) 
BlanchedAlmond#FFEBCDrgb (255,235,205)hsl(36,100%,90%) 
Blue#0000FFrgb (0,0,255)hsl(240,100%,50%) 
BlueViolet#8A2BE2rgb (138,43,226)hsl(271,76%,53%) 
Brown#A52A2Argb (165,42,42)hsl(0,59%,41%) 
BurlyWood#DEB887rgb (222,184,135)hsl(34,57%,70%) 
CadetBlue#5F9EA0rgb (95,158,160)hsl(182,25%,50%) 
Chartreuse#7FFF00rgb (127,255,0)hsl(90,100%,50%) 
Chocolate#D2691Ergb (210,105,30)hsl(25,75%,47%) 
Coral#FF7F50rgb (255,127,80)hsl(16,100%,66%) 
CornflowerBlue#6495EDrgb (100,149,237)hsl(219,79%,66%) 
Cornsilk#FFF8DCrgb (255,248,220)hsl(48,100%,93%) 
Crimson#DC143Crgb (220,20,60)hsl(348,83%,47%) 
Cyan#00FFFFrgb (0,255,255)hsl(180,100%,50%) 
DarkBlue#00008Brgb (0,0,139)hsl(240,100%,27%) 
DarkCyan#008B8Brgb (0,139,139)hsl(180,100%,27%) 
DarkGoldenRod#B8860Brgb (184,134,11)hsl(43,89%,38%) 
DarkGray#A9A9A9rgb (169,169,169)hsl(0,0%,66%) 
DarkGreen#006400rgb (0,100,0)hsl(120,100%,20%) 
DarkKhaki#BDB76Brgb (189,183,107)hsl(56,38%,58%) 
DarkMagenta#8B008Brgb (139,0,139)hsl(300,100%,27%) 
DarkOliveGreen#556B2Frgb (85,107,47)hsl(82,39%,30%) 
DarkOrange#FF8C00rgb (255,140,0)hsl(33,100%,50%) 
DarkOrchid#9932CCrgb (153,50,204)hsl(280,61%,50%) 
DarkRed#8B0000rgb (139,0,0)hsl(0,100%,27%) 
DarkSalmon#E9967Argb (233,150,122)hsl(15,72%,70%) 
DarkSeaGreen#8FBC8Frgb (143,188,143)hsl(120,25%,65%) 
DarkSlateBlue#483D8Brgb (72,61,139)hsl(248,39%,39%) 
DarkSlateGray#2F4F4Frgb (47,79,79)hsl(180,25%,25%) 
DarkTurquoise#00CED1rgb (0,206,209)hsl(181,100%,41%) 
DarkViolet#9400D3rgb (148,0,211)hsl(282,100%,41%) 
DeepPink#FF1493rgb (255,20,147)hsl(328,100%,54%) 
DeepSkyBlue#00BFFFrgb (0,191,255)hsl(195,100%,50%) 
DimGray#696969rgb (105,105,105)hsl(0,0%,41%) 
DodgerBlue#1E90FFrgb (30,144,255)hsl(210,100%,56%) 
FireBrick#B22222rgb (178,34,34)hsl(0,68%,42%) 
FloralWhite#FFFAF0rgb (255,250,240)hsl(40,100%,97%) 
ForestGreen#228B22rgb (34,139,34)hsl(120,61%,34%) 
Fuchsia#FF00FFrgb (255,0,255)hsl(300,100%,50%) 
Gainsboro#DCDCDCrgb (220,220,220)hsl(0,0%,86%) 
GhostWhite#F8F8FFrgb (248,248,255)hsl(240,100%,99%) 
Gold#FFD700rgb (255,215,0)hsl(51,100%,50%) 
GoldenRod#DAA520rgb (218,165,32)hsl(43,74%,49%) 
Gray#808080rgb (128,128,128)hsl(0,0%,50%) 
Green#008000rgb (0,128,0)hsl(120,100%,25%) 
GreenYellow#ADFF2Frgb (173,255,47)hsl(84,100%,59%) 
HoneyDew#F0FFF0rgb (240,255,240)hsl(120,100%,97%) 
HotPink#FF69B4rgb (255,105,180)hsl(330,100%,71%) 
IndianRed#CD5C5Crgb (205,92,92)hsl(0,53%,58%) 
Indigo#4B0082rgb (75,0,130)hsl(275,100%,25%) 
Ivory#FFFFF0rgb (255,255,240)hsl(60,100%,97%) 
Khaki#F0E68Crgb (240,230,140)hsl(54,77%,75%) 
Lavender#E6E6FArgb (230,230,250)hsl(240,67%,94%) 
LavenderBlush#FFF0F5rgb (255,240,245)hsl(340,100%,97%) 
LawnGreen#7CFC00rgb (124,252,0)hsl(90,100%,49%) 
LemonChiffon#FFFACDrgb (255,250,205)hsl(54,100%,90%) 
LightBlue#ADD8E6rgb (173,216,230)hsl(195,53%,79%) 
LightCoral#F08080rgb (240,128,128)hsl(0,79%,72%) 
LightCyan#E0FFFFrgb (224,255,255)hsl(180,100%,94%) 
LightGoldenRodYellow#FAFAD2rgb (250,250,210)hsl(60,80%,90%) 
LightGray#D3D3D3rgb (211,211,211)hsl(0,0%,83%) 
LightGreen#90EE90rgb (144,238,144)hsl(120,73%,75%) 
LightPink#FFB6C1rgb (255,182,193)hsl(351,100%,86%) 
LightSalmon#FFA07Argb (255,160,122)hsl(17,100%,74%) 
LightSeaGreen#20B2AArgb (32,178,170)hsl(177,70%,41%) 
LightSkyBlue#87CEFArgb (135,206,250)hsl(203,92%,75%) 
LightSlateGray#778899rgb (119,136,153)hsl(210,14%,53%) 
LightSteelBlue#B0C4DErgb (176,196,222)hsl(214,41%,78%) 
LightYellow#FFFFE0rgb (255,255,224)hsl(60,100%,94%) 
Lime#00FF00rgb (0,255,0)hsl(120,100%,50%) 
LimeGreen#32CD32rgb (50,205,50)hsl(120,61%,50%) 
Linen#FAF0E6rgb (250,240,230)hsl(30,67%,94%) 
Magenta#FF00FFrgb (255,0,255)hsl(300,100%,50%) 
Maroon#800000rgb (128,0,0)hsl(0,100%,25%) 
MediumAquaMarine#66CDAArgb (102,205,170)hsl(160,51%,60%) 
MediumBlue#0000CDrgb (0,0,205)hsl(240,100%,40%) 
MediumOrchid#BA55D3rgb (186,85,211)hsl(288,59%,58%) 
MediumPurple#9370DBrgb (147,112,219)hsl(260,60%,65%) 
MediumSeaGreen#3CB371rgb (60,179,113)hsl(147,50%,47%) 
MediumSlateBlue#7B68EErgb (123,104,238)hsl(249,80%,67%) 
MediumSpringGreen#00FA9Argb (0,250,154)hsl(157,100%,49%) 
MediumTurquoise#48D1CCrgb (72,209,204)hsl(178,60%,55%) 
MediumVioletRed#C71585rgb (199,21,133)hsl(322,81%,43%) 
MidnightBlue#191970rgb (25,25,112)hsl(240,64%,27%) 
MintCream#F5FFFArgb (245,255,250)hsl(150,100%,98%) 
MistyRose#FFE4E1rgb (255,228,225)hsl(6,100%,94%) 
Moccasin#FFE4B5rgb (255,228,181)hsl(38,100%,85%) 
NavajoWhite#FFDEADrgb (255,222,173)hsl(36,100%,84%) 
Navy#000080rgb (0,0,128)hsl(240,100%,25%) 
OldLace#FDF5E6rgb (253,245,230)hsl(39,85%,95%) 
Olive#808000rgb (128,128,0)hsl(60,100%,25%) 
OliveDrab#6B8E23rgb (107,142,35)hsl(80,60%,35%) 
Orange#FFA500rgb (255,165,0)hsl(39,100%,50%) 
OrangeRed#FF4500rgb (255,69,0)hsl(16,100%,50%) 
Orchid#DA70D6rgb (218,112,214)hsl(302,59%,65%) 
PaleGoldenRod#EEE8AArgb (238,232,170)hsl(55,67%,80%) 
PaleGreen#98FB98rgb (152,251,152)hsl(120,93%,79%) 
PaleTurquoise#AFEEEErgb (175,238,238)hsl(180,65%,81%) 
PaleVioletRed#DB7093rgb (219,112,147)hsl(340,60%,65%) 
PapayaWhip#FFEFD5rgb (255,239,213)hsl(37,100%,92%) 
PeachPuff#FFDAB9rgb (255,218,185)hsl(28,100%,86%) 
Peru#CD853Frgb (205,133,63)hsl(30,59%,53%) 
Pink#FFC0CBrgb (255,192,203)hsl(350,100%,88%) 
Plum#DDA0DDrgb (221,160,221)hsl(300,47%,75%) 
PowderBlue#B0E0E6rgb (176,224,230)hsl(187,52%,80%) 
Purple#800080rgb (128,0,128)hsl(300,100%,25%) 
RebeccaPurple#663399rgb (102,51,153)hsl(270,50%,40%) 
Red#FF0000rgb (255,0,0)hsl(0,100%,50%) 
RosyBrown#BC8F8Frgb (188,143,143)hsl(0,25%,65%) 
RoyalBlue#4169E1rgb (65,105,225)hsl(225,73%,57%) 
SaddleBrown#8B4513rgb (139,69,19)hsl(25,76%,31%) 
Salmon#FA8072rgb (250,128,114)hsl(6,93%,71%) 
SandyBrown#F4A460rgb (244,164,96)hsl(28,87%,67%) 
SeaGreen#2E8B57rgb (46,139,87)hsl(146,50%,36%) 
SeaShell#FFF5EErgb (255,245,238)hsl(25,100%,97%) 
Sienna#A0522Drgb (160,82,45)hsl(19,56%,40%) 
Silver#C0C0C0rgb (192,192,192)hsl(0,0%,75%) 
SkyBlue#87CEEBrgb (135,206,235)hsl(197,71%,73%) 
SlateBlue#6A5ACDrgb (106,90,205)hsl(248,53%,58%) 
SlateGray#708090rgb (112,128,144)hsl(210,13%,50%) 
Snow#FFFAFArgb (255,250,250)hsl(0,100%,99%) 
SpringGreen#00FF7Frgb (0,255,127)hsl(150,100%,50%) 
SteelBlue#4682B4rgb (70,130,180)hsl(207,44%,49%) 
Tan#D2B48Crgb (210,180,140)hsl(34,44%,69%) 
Teal#008080rgb (0,128,128)hsl(180,100%,25%) 
Thistle#D8BFD8rgb (216,191,216)hsl(300,24%,80%) 
Tomato#FF6347rgb (255,99,71)hsl(9,100%,64%) 
Turquoise#40E0D0rgb (64,224,208)hsl(174,72%,56%) 
Violet#EE82EErgb (238,130,238)hsl(300,76%,72%) 
Wheat#F5DEB3rgb (245,222,179)hsl(39,77%,83%) 
White#FFFFFFrgb (255,255,255)hsl(0,0%,100%) 
WhiteSmoke#F5F5F5rgb (245,245,245)hsl(0,0%,96%) 
Yellow#FFFF00rgb (255,255,0)hsl(60,100%,50%) 
YellowGreen#9ACD32rgb (154,205,50)hsl(80,61%,50%)