Colors in the CSS (and web generally) are divided into basic colors, web safe colors and the rest. By the name basic color we refer to the 16 colors that might be declared by using their names. The rest of the colors, including the so called "web safe" colors must be evoked through RGB (red, green, blue) / HSL (hue, saturation, lightness) representation or via their hexadecimal specification. The web safe colors used to be those colors that any browser will be able to render (255 of them). Since modern tools (user agents, screens...) are easily rendering pretty much any color put in front of them there is no need for paying special attention to them any more.

Below, there are the lists of the basic colors and shades of gray.

Basic colors
COLOR NAME COLOR HEX RGB
black   #000000 rgb(0,0,0)
silver   #c0c0c0 rgb(192,192,192)
gray   #808080 rgb(128,128,128)
white   #ffffff rgb(255,255,255)
maroon   #800000 rgb(128,0,0)
red   #ff0000 rgb(255,0,0)
purple   #800080 rgb(128,0,128)
fuchsia   #ff00ff rgb(255,0,255)
green   #008000 rgb(0,128,0)
lime   #00ff00 rgb(0,255,0)
olive   #808000 rgb(128,128,0)
yellow   #ffff00 rgb(255,255,0)
navy   #000080 rgb(0,0,128)
blue   #0000ff rgb(0,0,255)
teal   #008080 rgb(0,128,128)
aqua   #00ffff rgb(0,255,255)

Shades of gray
SHADES HEX RGB
  #000000 rgb(0,0,0)
  #080808 rgb(8,8,8)
  #101010 rgb(16,16,16)
  #181818 rgb(24,24,24)
  #202020 rgb(32,32,32)
  #282828 rgb(40,40,40)
  #303030 rgb(48,48,48)
  #383838 rgb(56,56,56)
  #404040 rgb(64,64,64)
  #484848 rgb(72,72,72)
  #505050 rgb(80,80,80)
  #585858 rgb(88,88,88)
  #606060 rgb(96,96,96)
  #686868 rgb(104,104,104)
  #707070 rgb(112,112,112)
  #787878 rgb(120,120,120)
  #808080 rgb(128,128,128)
  #888888 rgb(136,136,136)
  #909090 rgb(144,144,144)
  #989898 rgb(152,152,152)
  #a0a0a0 rgb(160,160,160)
  #a8a8a8 rgb(168,168,168)
  #b0b0b0 rgb(176,176,176)
  #b8b8b8 rgb(184,184,184)
  #c0c0c0 rgb(192,192,192)
  #c8c8c8 rgb(200,200,200)
  #d0d0d0 rgb(208,208,208)
  #d8d8d8 rgb(216,216,216)
  #e0e0e0 rgb(224,224,224)
  #e8e8e8 rgb(232,232,232)
  #f0f0f0 rgb(240,240,240)
  #f8f8f8 rgb(248,248,248)
  #ffffff rgb(255,255,255)