KCU::tint suggested improvements

[Matthew Woehlke]

I've noticed a few concerns as of late regarding KColorScheme's extended 
background colors (mainly from Anders and, honestly, myself ;-) ), so I 
decided to take a few minutes to play with it and see if I could make 
things better. The attached patch *seriously* reduces the amount of 
luma-change of the base color, which seems to result in much more 
homogenous tints for a particular base and amount, regardless of the 
tint color. This hopefully will provide much more usable behavior with 
varying color schemes.

Please review and let me know if it's OK to commit this. CC'ing 
usability, as I'd love to hear any thoughts from them on this matter 
(which very much relates to u7y/a11y).

Please see trunk/playground/libs/ui/kcolor/tinttest for a demonstration 
of the old vs. new algorithms; it should compile with a simple 'cmake 
/path/to/source && make' (it is not meant to be 'make install'd; just 
run from the build dir).

Anders: if anything this seems to make ActiveBackground in Oxygen scheme 
even less obvious :-/, but the contrast with ActiveText is better (the 
idea was to address insufficient contrast between FooBackground and 
FooText, and also some cases where NormalBackground and FooBackground 
have too *much* contrast).

-- 
Matthew
References: The references have been deleted in order to protect the 
guilty and avoid enriching the lawyers. -- RFC 1925
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