Re: how blue must blue be for blue-on-yellow color scheme?

Hello,

On Montag, 21. Januar 2008, Matthew Woehlke wrote:
> [...]
> Ok, so I keep hearing that blue-on-yellow colors are for a11y
> specifically... that being the case, I suppose I'm going to go ahead and
> add that scheme to kdea11y.

I created all three high-contrast themes (black on white, white on black, 
and yellow on blue) for KDE 3.x after I read somewhere that they are 
necessary. However, I did not really ask for specific reasons at that 
time, and the only color scheme where I had input from people with low 
vision is the white-on-black color scheme, so I do not know whether the 
yellow-on-blue color scheme really meets the needs of those persons that 
may need such a color scheme.

> What doesn't entirely make sense to me is what's wrong with
> white-on-black for most cases (rod deficiencies as opposed to cone
> deficiencies, where someone can tell about colors but not lightnesses?).
> Anyway... how important is it that the blue be #0000ff as opposed to
> #0000c0 and there-abouts?

I would guess that people with rod deficiencies are unusual. From my basic 
knowlodge about how the eye works I would guess that even these people can 
tell the difference between white and black, but they might not be able to 
differentiate different shades of gray that easily.

I know, however, that there are people that need a high contrast, mostly 
dark color scheme, but for whom white text on a black background is a too 
large contrast (they are dazzled by the white and therefore cannot read 
what is written). I would expect that the yellow-on-blue color scheme is 
needed for these persons as yellow is darker than white (and brighter than 
blue) and blue is brighter than black (and darker than yellow).

> Put another way, would the scheme in [1] (that tries to balance being
> blue-on-yellow with "something that won't cause blindness in 'normal'
> people ;-)") be adequate, or do things really, really need to be
> #ffff00-on-#0000ff?
>
> 1: http://img178.imageshack.us/img178/3632/olympusrh8.png

As I have said above, I created the yellow-on-blue color scheme without 
feedback from users of it. In fact, it is a modification of an earlier 
version of the white-on-black color scheme where white is replaced by 
yellow and blue is replaced by black.

If my assumption about possible users of the color scheme is correct, I 
would argue that the scheme you suggest is problematic in the way that it 
increases the contrast of the yellow-on-blue color scheme by partly 
lightening the yellow and partly darkening the blue.

That said, the theme looks much better than my attempt on a yellow-on-blue 
color scheme to my non-impairmed eyes (but as I said, it may not be what 
the users of a yellow-on-blue color scheme need).


> Matt Blissett [...] noted that the selection could use more contrast
> (actually,  there is already more contrast than in the KDE3 version,
> but it's still not very good). What's the safest way to do that; make
> the selection  lighter, or everything else darker? Or is it "good enough"
> and changing it is likely to cause problems?

Please keep in mind that persons with low vision need a good contrast 
between the text and the background color in order to be able to read. 
Differentiating the brightness between two different shades of background 
colors can be done with a far smaller difference than reading text.

I hope that my comments are usefull for you,

Gunnar Schmi Dt
-- 
Co-maintainer of the KDE Accessibility Project
Maintainer of the kdeaccessibility package
http://accessibility.kde.org/

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