Accessible Colors | Accessibility

Simply put you can say, color blind people see the world like people with normal color vision see it at dusk or dawn. At this time of the day colors start to fade away which is comparable to a color vision deficiency.

http://www.colblindor.com/2010/03/09/types-of-color-blindness/

Primary Colors and the Varying Flavors of Color Blindness

Protanopia is the absence of red sensitivity, also referred to as red dichromacy. It's the result of the loss of function of the L cones, which provide us with sensitivity to the red portion of the visible spectrum. With red being at the end of the visible spectrum, there is only a partial overlap of sensitivity with the two other types of cones, and so people with Protanopia have a distinct loss of sensitivity to light at the red end of the spectrum.

Protanopia is red weakness, and occurs when the L-cones are functioning, but not at the levels they should be.; Protanomalia affects approximately 1 percent of the male population.

Deuteranopia affects approximately 1.1 percent of the male population and is the absence of green sensitivity, also referred to as green dichromacy. It is the result of the loss of function of the M-cones, which provide us with sensitivity to the green portion of the visible spectrum. Due to the location of green in the spectrum, to the actual sensitivity overlap between the M-cones (green) and L-cones (red), and to the partial overlap with the S-cones (blue), people with Deuteranopia have a fairly normal level of sensitivity throughout the spectrum, although they will still experience confusion among the individual colors.

Deuteranomalia affects approximately 4.9 percent of male population and is green weakness, and occurs when the M-cones are functioning, but not at the levels they should be.

A Deuteranope is one who is afflicted with a form of red/green color deficit (Deuteranomalia).

Tritanopia affects approximately 0.001 percent of the male population and is the absence of blue sensitivity, also referred to as blue dichromacy. Tritanopia is the least common of all forms of color-vision deficiencies, and is the result of the loss of functionality of the S-Cones, which provide sensitivity to the blue portion of the visible spectrum. Because blue is at the opposite end of the spectrum from red, and because the sensitivity of the S-cones has less overlap with the other two cones, people with Tritanopia have a much more severe loss of sensitivity across the spectrum.

Tritanomalia would refer to blue weakness, but there don't appear to be any reported cases of this as a form of color deficiency. This could be because, overall, the S-cones make up only 10 percent of the cones in the eye; by the time an abnormality is perceptible, the cones are, for the most part, non-functional.

How the Primary Colors Look to a Persoon that is not Color Blind (Regular).

How the Primary Colors Look to Someone with Protanope (Another Form of Red/Green Color Deficit).

How the Primary Colors Look to Someone with Deuteranopia (Green Blind).

How the Primary Colors Look to Someone with Tritanope (Blue/Yellow Deficit - very rare).

Four Types

• Trichromacy
• Dichromacy
• Anomalous Trichromacy
• Monochromacy

Monitor Color Resolution

A correct perception of color is very important for a11y, usability, etc. Check your color resolution:

list of the more common display color resolutions and the kind of visual results you can expect from them:

True color (24bit or 32bit - 16M colors)	High color (15 or 16bit - Up to 64K colors)	16 or 256 colors
Right color resolution to fully appreciate on-screen colors. Everything higher than 24bit resolution is fine but from a practical point of view is just nonsense.	You'll loose some color definition but you can still have good results. Probably if you compare a monitor using this resolution with a 24bit counterpart, you will not be able to detect any great difference. Monitor settings play a much important role in digital color perception.	You will not be able to correctly see on-screen colors, they will tend to melt together and look all alike. You can anyway use all the color numeric data resulting from the use of the different site services.

All the color tables (below) look different:

Your system is able to visualize 16M colors. Keep in mind that the color difference between the first 2 tables is very subtle.

The 16M and 64K tables are very similar:

With a 15/16bit video card you should be able to detect dithered colors on the 16M table.

All the tables have the same colors:

Sorry you have a 256 colors (or less) video system.

Monitor Color Resolution

References and Resources

• Acquired Versus Congenital Colour Deficiencies
• Testing Color Vision
• Designing Accessible Color Spectrums
• Do's and Don'ts of Colour
• The Accessibility of Color on the Web
• Vision Simulator - How do things look to people with colorblindness or cataracts?
• Corrective Lenses for the Colorblind

Ensure that foreground and background color combinations provide sufficient contrast when viewed by someone having color defecits or when viewed on a black and white screen.

Color visibility can be determined according to the following alogirithm:

Two colors provide good visibility if the brightness difference and the color difference between the two colors are greater than a set range.

color a + color b = good visibility() {
((bright difference) + (color difference)) > set range;
}

Color Brightness

Color brightness can be determined by the following formula:

Note:This algorithim is taken from a formula for converting rgb values to YIQ values. This brightness value gives a perceived brightness for the color.

Color Difference

Color difference can be determined by the following formula:

(maximum (Red Value 1, Red Value 2) - minimum (Red Value 1, Red Value 12)) + (maximum(Green Value 1, Green Value 2)) + (maximum(Blue Value 1, Blue Value 2) - minimum (Blue Value 1, Blue Value 2))

The range for color brightness difference is 125; the range for color difference is 500.

Color Contrast - Test File

Contrast Ratio

Contrast ratio became w3c recommendation in 2008 to help determine whether or not the contrast between two colors can be read by people with color blindness or other visual impairments

Contrast ratio:measure the relative luminance of each letter (unless they're all uniform) using the formula:

L = 0.216*R + 0.7152*G + 0.0722*B; where R, G and B are defined as:
if RsRGB <= 0.03928 then R = RsRGB/12.92 else R = ((RsRGB+0.055)/1.055) ^ 2.4
 ◦ if GsRGB <= 0.03928 then G = GsRGB/12.92 else G = ((GsRGB+0.055)/1.055) ^ 2.4
 ◦ if BsRGB <= 0.03928 then B = BsRGB/12.92 else B = ((BsRGB+0.055)/1.055) ^ 2.4
 ◦ and RsRGB, GsRGB, and BsRGB are defined as:
 ◦ RsRGB = R8bit/255
 ◦ GsRGB = G8bit/255
 ◦ BsRGB = B8bit/255

The ^ character is the exponentiation operator.

Note:For aliased letters, use the relative luminance value found two pixels in from the edge of the letter.

Color Brightness Formula

((Read value X 299) + (Green value X 587) + (Blue value X 114)) / 1000

difference between background brightness and foreground brightness should be great than 125.

Note:this algorithim is taken from a formula for converting rgb values to YIQ values..... This brightness value gives a perceived brightness for a color

Color Difference Formula

Colour difference is determined by the following formula:

(maximum (Red value 1, Red value 2) - minimum (Red value 1, Red value 2)) + (maximum (Green value 1, Green value 2) - minimum (Green value 1, Green value 2)) + (maximum (Blue value 1, Blue value 2) - minimum (Blue value 1, Blue value 2))

The difference between the background colour and the foreground colour should be greater than 500.

ColourMap - Colour Blind Helper

To install the toolbar, download the setup file colourmap.zip. The zip file contains a single file "colourmap.xpi". Unzip to desktop, start up Firefox, drag colourmap.xpi into the main window area of Firefox and let Firefox restart.

Color Design for the Color Vision Impaired

Designing Maps for the Colour-Vision Impaired

Color Tools

ca (Contrast Analyser)

ca is useful to help determine, in particular, the legibility of text on a web page and the legibility of image based representations of text.

• Colour Contrast Checker
• Colorblind Web Page Filter
• Color Laboratory

Vischeck

Vischeck simulates colorblind vision in-browser; run Vischeck on a web page or run it VischeckImageon your own images.

Daltonize

Daltonize corrects images for colorblind viewers and functions in-browser.