Temperature to color

<?

include 'misc.inc';

for ($temp = -5; $temp < 5; $temp += 0.5)
{
    $red = atan($temp) / 3.141593 + 0.5;
    $blue = 1 - $red;
    $green = $red*0.3 + $blue*0.7;
    $red = $red*255;
    $green = $green*255;
    $blue = $blue*255;

    $colorcode = RGBtoHtmlColor($red, $green, $blue);
    printf("temperature %+.02f = RGB %03.0f, %03.0f, %03.0f (#%s)\n", $temp, $red, $green, $blue, $colorcode);
}

?>