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The classic colormap of fire (and that of black body radiation too) is a very simple function within the RGB world.

fire  R   G   B
  0   0   0   0
  1   3   0   0
  2   6   0   0
  .   .   .   .
 84 252   0   0
 85 255   0   0
 86 255   3   0
  .   .   .   .
169 255 252   0
170 255 255   0
171 255 255   3
  .   .   .   .
254 255 255 252
255 255 255 255

The function (in pseudo code - translate to your favorite language as desired):

fire(intensity {range: 0 - 255})
  R = min(intensity,85) * 3
  intensity = max(intensity-85,0)
  G = min(intensity,85) * 3
  intensity = max(intensity-85,0)
  B = min(intensity,85) * 3
  return (R,G,B)

This colormap ranges in intensity from black through dark red, to orange and yellow and eventually to a bright white.

Realize that one 'feature' of this color map is that it has exactly 256 colors, which is the maximum number allowed by the .gif file format. If you desire to make a flame (render, draw, animate) in a .gif, this colormap will serve you well.

Of interest - the following html colors closely match a color above:

fire  R   G   B | color         R   G   B   | dR  dG  dB
  0   0   0   0 | BLACK         0   0   0   |  0   0   0
 85 255   0   0 | RED         255   0   0   |  0   0   0
108 255  69   0 | ORAGERED    255  69   0   |  0   0   0
127 255 126   0 | darkorange1 255 127   0   |  0  -1   0
132 255 141   0 | DARKORANGE  255 140   0   |  0  +1   0
140 255 165   0 | ORANGE      255 165   0   |  0   0   0
157 255 216   0 | GOLD        255 215   0   |  0  +1   0
170 255 255   0 | YELLOW      255 255   0   |  0   0   0
245 255 255 225 | LIGHTYELLOW 255 255 224   |  0  +1   0
250 255 255 240 | IVORY       255 255 240   |  0   0   0
255 255 255 255 | WHITE       255 255 255   |  0   0   0
(standard html colors are in CAPS)

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