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redgreenblue is a simple Ruby library for handling RGB colors.

It lets you express RGB colors as 24-bit triplets, 48-bit triplets, fractions, or hexadecimal notation, as well as HSL, HSB, or HSV (hue, saturation, and lightness, brightness, or value), and has 148 named CSS colors built-in.

redgreenblue can output RGB colors as CIE XYZ or xyY coordinates, L*a*b*, L*u*v*, and their cylindrical representations LCHab and LCHuv.

If your terminal supports "true color", redgreenblue's colorised inspect styles will display your colors in 24-bit splendour, right in the terminal.

redgreenblue can create 1-pixel GIF's from any color and also understands some more exotic formats, such as 16-bit RGB565 and 24-bit BGR. On a Mac it can interact with the system color picker.

redgreenblue is available as a gem. You can simply install it with:

gem install redgreenblue

redgreenblue has no dependencies outside the Ruby Standard Library, and works with Ruby 2.2 or newer.

Let's create an RGB color:

require 'redgreenblue'
=> true
pink = RGB.hex('ff99cc')
=> RGB #ff99cc (red=1.00000 green=0.60000 blue=0.80000)
pink.class
=> RGB::Color

There are many ways to create RGB::Color objects.

These six examples will create the exact same color:

pink = RGB.hex('f9c')
pink = RGB.new(1, 0.6, 0.8)
pink = RGB.rgb(255, 153, 204)
pink = RGB.rrggbb(65535, 39321, 52428)
pink = RGB.hsl(330, 1, 0.8)
pink = RGB.hsv(330, 0.4, 1)

An RGB::Color object can supply many pieces of information about itself.

For example:

pink.hex
=> "ff99cc"
pink.hex(true)
=> "f9c"
pink.values
=> [1.0, 0.6, 0.8]
pink.red
=> 1.0
pink.rgb
=> [255, 153, 204]
pink.r
=> 255
pink.rrggbb
=> [65535, 39321, 52428]
pink.hsl
=> [330.0, 1.0, 0.8]
pink.hsb
=> [330.0, 0.4, 1.0]
pink.hwb
=> [330.0, 0.6, 0.0]
pink.cie_xyz
=> [0.635314, 0.484064, 0.631122]
pink.cie_lab
=> [75.08050605, 44.58467493, -9.72046865]

RGB::Color objects can easily be changed: they are mutable:

rose = RGB.red
=> RGB #ff0000 (red=1.00000 green=0.00000 blue=0.00000)
rose.whiten!(0.6)
=> RGB #ff9999 (red=1.00000 green=0.60000 blue=0.60000)
rose.hsl_rotate!(-30)
=> RGB #ff99cc (red=1.00000 green=0.60000 blue=0.80000)
rose == pink
=> true

• HSL and HSV on Wikipedia
• Photoshop by the Numbers: Color Coding, by Gerald Bakker
• Das ABC der Farbe, by Markus Wäger (2017), ISBN 978-3-8362-4501-2
• Bruce Lindbloom
• CIE 15: Technical Report: Colorimetry, 3rd edition (2004)
• A Guided Tour of Color Space (PDF), by Charles Poynton (1997)
• Color for the Sciences, by Jan Koenderink (2010), ISBN 978-0-262-01428-1
• Color Ordered, by Rolf Kuehni and Andreas Schwarz (2008), ISBN 978-0-19-518968-1
• Psychology, by Henry Gleitman, James Gross, Daniel Reisberg (2010), ISBN 978-0-393-93250-8
• Interaction of Color, by Josef Albers (1963), ISBN 978-0-300-17935-4
• 配色事典 – A Dictionary of Color Combinations, by Sanzo Wada (2010), ISBN 978-4-86152-247-5
• The Anatomy of Colour, by Patrick Baty (2017), ISBN 978-0-500-51933-2
• Nature's Palette, by Patrick Baty (2021), ISBN 978-0-500-25246-8
• Einführung in die Farbenlehre, by Harald Küppers (2016), ISBN 978-3-8321-6403-4

Apart from the resources listed above, some discussions and answers on Stack Overflow and PerlMonks were very helpful, as were some articles on Wikipedia. Many helpful sources of information are credited where applicable in the source code, often with a link.

Gamma- and CIE-processing in redgreenblue lean heavily on work by Bruce Lindbloom.

See the included LICENSE.txt file.

Color: a versatile Ruby color library.

“The philosopher for whom rainbows can be explained away never saw them.”

Henry David Thoreau, Journal, 5 November 1857.