How to generate random 'greenish' colors

Simple solution: Use the HSL or HSV color space instead of rgb (convert it to RGB afterwards if you need this). The difference is the meaning of the tuple: Where RGB means values for Red, Green and Blue, in HSL the H is the color (120 degree or 0.33 meaning green for example) and the S is for saturation and the V for the brightness. So keep the H at a fixed value (or for even more random colors you could randomize it by add/sub a small random number) and randomize the S and the V. See the wikipedia article.

As others have suggested, generating random colours is much easier in the HSV colour space (or HSL, the difference is pretty irrelevant for this)

So, code to generate random "green'ish" colours, and (for demonstration purposes) display them as a series of simple coloured HTML span tags:

#!/usr/bin/env python2.5"""Random green colour generator, written by dbr, forhttp://stackoverflow.com/questions/1586147/how-to-generate-random-greenish-colors"""def hsv_to_rgb(h, s, v):    """Converts HSV value to RGB values    Hue is in range 0-359 (degrees), value/saturation are in range 0-1 (float)    Direct implementation of:    http://en.wikipedia.org/wiki/HSL_and_HSV#Conversion_from_HSV_to_RGB    """    h, s, v = [float(x) for x in (h, s, v)]    hi = (h / 60) % 6    hi = int(round(hi))    f = (h / 60) - (h / 60)    p = v * (1 - s)    q = v * (1 - f * s)    t = v * (1 - (1 - f) * s)    if hi == 0:        return v, t, p    elif hi == 1:        return q, v, p    elif hi == 2:        return p, v, t    elif hi == 3:        return p, q, v    elif hi == 4:        return t, p, v    elif hi == 5:        return v, p, qdef test():    """Check examples on..    http://en.wikipedia.org/wiki/HSL_and_HSV#Examples    ..work correctly    """    def verify(got, expected):        if got != expected:            raise AssertionError("Got %s, expected %s" % (got, expected))    verify(hsv_to_rgb(0, 1, 1), (1, 0, 0))    verify(hsv_to_rgb(120, 0.5, 1.0), (0.5, 1, 0.5))    verify(hsv_to_rgb(240, 1, 0.5), (0, 0, 0.5))def main():    """Generate 50 random RGB colours, and create some simple coloured HTML    span tags to verify them.    """    test() # Run simple test suite    from random import randint, uniform    for i in range(50):        # Tweak these values to change colours/variance        h = randint(90, 140) # Select random green'ish hue from hue wheel        s = uniform(0.2, 1)        v = uniform(0.3, 1)        r, g, b = hsv_to_rgb(h, s, v)        # Convert to 0-1 range for HTML output        r, g, b = [x*255 for x in (r, g, b)]        print "<span style='background:rgb(%i, %i, %i)'>  </span>" % (r, g, b)if __name__ == '__main__':    main()

The output (when viewed in a web-browser) should look something along the lines of:

Edit: I didn't know about the colorsys module. Instead of the above hsv_to_rgb function, you could use colorsys.hsv_to_rgb, which makes the code much shorter (it's not quite a drop-in replacement, as my hsv_to_rgb function expects the hue to be in degrees instead of 0-1):

#!/usr/bin/env python2.5from colorsys import hsv_to_rgbfrom random import randint, uniformfor x in range(50):    h = uniform(0.25, 0.38) # Select random green'ish hue from hue wheel    s = uniform(0.2, 1)    v = uniform(0.3, 1)    r, g, b = hsv_to_rgb(h, s, v)    # Convert to 0-1 range for HTML output    r, g, b = [x*255 for x in (r, g, b)]    print "<span style='background:rgb(%i, %i, %i)'>  </span>" % (r, g, b)

Check out the colorsys module:

http://docs.python.org/library/colorsys.html

Use the HSL or HSV color space. Randomize the hue to be close to green, then choose completely random stuff for the saturation and V (brightness).