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>Colors in X Window System</A
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> In X Window system, each color is described by 3 numbers,
      namely the contents of Red, Green and Blue (as is well known,
      every color can be obtained by combining these three primary
      colors). These 3 values are commonly called the RGB
      values. Usually each of them is allowed to range from 0 to 255;
      for example, triple (0,0,0) is black, (255,0,0) is pure red, and
      (255, 255, 255) is white.  
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> The total number of possible colors is thus
      256×256×256=2<SUP
>24</SUP
>=16,777,216.
      Of course, whether or not your system is actually able to show
      that many different colors depends on the configuration of X
      Window system, which is limited by the capabilities of your
      video card. Most modern video cards are capable of showing all
      these colors; some older cards will only be able to use
      2<SUP
>16</SUP
>=64,536 (colordepth 16) or even
      2<SUP
>8</SUP
>=256 (colordepth 8) colors. In this
      case, X Window System will still use triples like (234, 112,
      243) for describing RGB values, but some of these triples will
      produce identical colors. More information about colors can be
      found in the manual page for X. 
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