Terminal output colors in python

term_colors.py

from __future__ import print_function
"""
Utilities for 256 color support in terminals.

Adapted from:
http://stackoverflow.com/questions/1403353/256-color-terminal-library-for-ruby

The color palette is indexed as follows:

0-15: System colors
    0  black         8  dark gray
    1  red           9  bright red
    2  green         10 bright green
    3  yellow        11 bright yellow
    4  blue          12 bright blue
    5  magenta       13 bright magenta
    6  cyan          14 bright cyan
    7  light gray    15 white

16-231: 6x6x6 Color Cube
    All combinations of red, green, and blue from 0 to 5.

232-255: Grayscale Ramp
    24 shades of gray, not including black and white.
"""

# System color name constants.
(
    BLACK,
    RED,
    GREEN,
    YELLOW,
    BLUE,
    MAGENTA,
    CYAN,
    LIGHT_GRAY,
    DARK_GRAY,
    BRIGHT_RED,
    BRIGHT_GREEN,
    BRIGHT_YELLOW,
    BRIGHT_BLUE,
    BRIGHT_MAGENTA,
    BRIGHT_CYAN,
    WHITE,
) = range(16)

def rgb(red, green, blue):
    """
    Calculate the palette index of a color in the 6x6x6 color cube.

    The red, green and blue arguments may range from 0 to 5.
    """
    return 16 + (red * 36) + (green * 6) + blue

def gray(value):
    """
    Calculate the palette index of a color in the grayscale ramp.

    The value argument may range from 0 to 23.
    """
    return 232 + value

def set_color(fg=None, bg=None):
    """
    Print escape codes to set the terminal color.

    fg and bg are indices into the color palette for the foreground and
    background colors.
    """
    print(_set_color(fg, bg), end='')

def _set_color(fg=None, bg=None):
    result = ''
    if fg:
        result += '\x1b[38;5;%dm' % fg
    if bg:
        result += '\x1b[48;5;%dm' % bg
    return result

def reset_color():
    """
    Reset terminal color to default.
    """
    print(_reset_color(), end='')

def _reset_color():
    return '\x1b[0m'

def print_color(*args, **kwargs):
    """
    Print function, with extra arguments fg and bg to set colors.
    """
    fg = kwargs.pop('fg', None)
    bg = kwargs.pop('bg', None)
    set_color(fg, bg)
    print(*args, **kwargs)
    reset_color()

def format_color(string, fg=None, bg=None):
    return _set_color(fg, bg) + string + _reset_color()

if __name__ == '__main__':
    # Print a test graphic showing all colors.

    print('System colors:')
    for c in range(8):
        print_color('  ', bg=c, end='')
    print()
    for c in range(8, 16):
        print_color('  ', bg=c, end='')
    print()
    print()

    print('RGB color cube, 6x6x6:')
    for green in range(6):
        for red in range(6):
            for blue in range(6):
                print_color('  ', bg=rgb(red, green, blue), end='')
            print(' ', end='')
        print()
    print()

    print('Grayscale ramp, with RGB grays:')
    for value in range(24):
        print_color('  ', bg=gray(value), end='')
    print()

    print_color('  ', bg=rgb(0, 0, 0), end='')
    print('  '*7, end='')
    print_color('    ', bg=rgb(1, 1, 1), end='')
    print('  '*2, end='')
    print_color('    ', bg=rgb(2, 2, 2), end='')
    print('  '*2, end='')
    print_color('    ', bg=rgb(3, 3, 3), end='')
    print('  '*2, end='')
    print_color('    ', bg=rgb(4, 4, 4), end='')
    print('  ', end='')
    print_color('  ', bg=rgb(5, 5, 5), end='')
    print()

Is it intended that in line 115 - 117 you iterate over green first, then red and then blue? I would expect to loop over red, green and then blue, because that would result in an ascending order by value of rgb(red, green, blue).

KDE's konsole is doing it that way, too. And they also calculate the index as 16 + ($red * 36) + ($green * 6) + $blue, so they also print the colors in non-ascending order.