[RFC] Color usability time, take 2

[Olaf Schmidt]

Hi Matthew!

Thanks a lot for working on this!

This is truly important for accessibility.

> Also the foreground roles (names, suggested uses) are certainly not set
> in stone yet.

Yes, I agree.

A quick explanation why we ended up suggesting 7 additional foreground and 7 
additional background colours:

* Many applications need more colours, but we cannot create a new specific 
colour role for every single purpose. By using assigning "suggested purposes" 
we achieve consistency while keeping the new roles general enough for wider 
use.

* There are about eight main colours: red, brown, orange, yellow, green, cyan, 
blue, magenta. If we use one as a focus colour, then we have 7 left.

Users for the background colours would be for example Kate, Konqueror (address 
bar) and Kalzium.

Users of the foreground colours would be for example Kate, Kontact, Kalzium, 
Konversation, and many more.

The additional foreground colours need to be available for all of the five 
backgrounds (view, window, button, selected, tooltip), i.e. either
a) the colour scheme needs to pick colours that work for all, or
b) multiply the number of colours by five, or
c) we use HSY colour manipulations to increase the contrast if needed

Using colour manipulations to get the 7 additional background colours is 
probably less reliable to achieve a good result, but I do not really care as 
long as enough contrast is ensured according to the WACG2 guidelines, cf. 
http://accessibility.kde.org/oxygen.php (BTW, my self-invented sHSL seems to 
be identical to HSY).

Olaf