from ADV-HTML LISTSERV: color blind people and link colors
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Date: Thu, 13 Jun 1996 11:57:09 -0700
From: Samu Mielonen
Subject: COMMENT: Colour Blind People and Link Colours
>We should definitely be concerned about changing link colours, (and of
>course, text and background colours) of our web pages.
Having an anomalous trichromatic colour vision myself and having used
WWW extensively since '93 I know that most of you
don't think about color blinds for a second :)
And I can't really blame you... Designing for people with deficit color
vision like myself is complicated. It's not a matter of green/blue or
yellow/blue combinations, which happen to be dichromatic color
vision deficiencies. There's also total color blindness called
aptly monochromatism (very rare). The third group of "color blinds"
have anomalous trichromatism and have one or more of their primary color
(R G B) sensing cones on their retina deficient at certain wavelength(s).
This results in a much more complicated color confusion than with
duochromatism. And as anomalous trichromats are probably the biggest
group of color blinds, this makes designers life tricky.
I for example may confuse green with brown, blue with purple, yellow with
green, ad nauseaum. The key here is understanding color space and what
enables us to distinguish colors apart.
You can understand color by it's three different components:
hue, saturation and lightness. Think of the standard Mac
color picker that has a circle in it and a slider at the
bottom that washes or darkens out the colors in the circle.
In that circle:
Hue (color) is the color at the edge of the circle. By dragging
your cursor around the edge of the circle you notice how only the
hue changes and ligtness and saturation keep the same.
Saturation (colorfulness) is the purity of the specified
color. This is shown as how near the edge your color is. The
closer to the edge of the circle, the more chroma you have.
Closer to the center you move, the less chroma you have.
Lightness (brightness) is the intensity of the light that
a surface or emitter reflects. The less lightness you have,
the blacker/darker the image/color will look and vice
versa. On the Mac color wheel this is shown as the
slider under the wheel that makes the colors appear from
black to full intensity and again to white.
Ok, so how does all this relate to anomalous trichromatism?
Well, as you can't really predict what the kind of
color deficiency each person has, you must count on other
factors than the hue to make your colors distinguishable
from each other.
How can you do this? Well, by specifying differing
lightness values at big enough intervals (absolute 20% jumps,
when 0% is min and 100% is max) and using as pure colors
as your design makes possible (maximum saturation that
you can use to make the color still be readable).
The problem with very intense colors with 100% saturation
are psychological effects, like ghost images, after images,
irritability, etc. So, having a bright red on a bright blue
background might not be a good idea for text that you actually
want people to read. Try walking the middle ground here. Make the
other color quite saturated (preferably not the text) and the other
less so. And the less of saturation difference you have between
two colors that must be distinguished from each other the more
lightness difference you must have between them.
And finally, to give a quick test to your design: Turn your
monitor to 256 shades of grey and take a look at your design:
- Can you distinguish the different colors now yourself on
the basis of their lightness values? Better yet, can somebody
else who has not designed your screen make the difference?
- Is the text pleasant to read or does it tire you?
- Are you using too many different colors (ligthness values)
that just confuse the reader without adding information to
your design?
- Check for blue/yellow and red/green combinations. If you
use these color pairs to distinguish information, you're
in trouble with dichromatism.
If you have trouble with some of the above tests, you probably
should tweak your design. Increase lightness contrasts between
colors, reduce the number of colors if possible, use less/more
saturated colors and use your own judgement. Once you start
to think about these issues, you'll notice that you'll become
more aware of them and can perceive things you didn't notice
before...
I hope that clears some of the issues on color deficit vision.
If you feel like you want to know more about color spaces (like
HSL) I suggest you take a look at the Color Space FAQ that also
talks about these things more in-depth:
http://www.well.com/user/rld/vidpage/color_faq.html
Best regards,
Samu Mielonen
--
(C) 1996 Samu Mielonen. All rights
"All I wanna be is smarter than my enemy
All I wanna have is everything I haven't got
All I wanna take is everything ever made." IF, 'Saturdays Angels'
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From: "Martin E. Modell"
Subject: COMMENT: Colour Blind People and Link Colours
I would like to add something to the message below. I am also color blind, but
my particular symptoms are reflected in shade blindness. That is I can see
primary colors, but have a difficult to impossible time seeing or
distinguishing between shades of a color, or between shades of different
colors. To illustrate:
I have a great deal of difficulty distinguishing between the different
temperature band colors on the temperature maps of the TV news shows.
I cannot distinguish between the various color bands on standard elevation
(altitude) maps.
I can't see Red on Black, Blue on Black, Red on Green, or colors of the same
intensity on anything. I cannot see the numbers/letters on the standard color
blindness test flipchart.
It further manifests itself in that I am not bothered by color combinations
which seem to drive other people wild. (light green, chartruse(?) and yellow
all look the same to me, as do blue/purple, magenta, etc.) I have had people
turn in revulsion at the colors I used on my windows color scheme.
I have browsed hundreds, maybe even a thousand pages, and many are constructed
with colors which I cannot see at all.
And when I hit a link which changes colors sometimes they "disappear" from my
sight. I know that creativity is to be encouraged, but I for one would
appreciate seeing a page/guide of "acceptable" or "recommended" color
combinations, If only for those of us who would like to put color on our pages
but who are afraid to publish without someone reviewing our color choices
before hand.
TIA Marty Modell
Marty Modell e-mail: ir001264@interramp.com
Of all the sins of technology, arrogance is the worst
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Date: Thu, 13 Jun 1996 11:58:03 -0700
From: "gunnar@this.is"
Subject: COMMENT: Colour Blind People and Link Colours
:->Subject: COMMENT: Colour Blind People and Link Colours
:->
:->>Should we be concerned about changing link colors -- particularly to red --
:->>given color-blindness??
:->
:->Kathy,
IMHO, we should. When designing pages that don't require specific colors to
harmonize with the design in general, I always use ff0000 for link and
0000ff for vlink. This is not based on any knowledge for color blindness, I
just don't like the purple color which is Netscapes color for vlink and also
find it logical to equate
red with hot exciting and
blue with cold I've already seen it.
Any input on good vlink colors (for colorblind people) would be much
appreciated.
--
bye . . .
gunnar@this.is . . .
http://this.is/gunnar . . .
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