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I found the default colors readable and do not see a gray font on a gray background. For my taste the colors are even to much toned down and I usually change the colors from Oxygen to Norway, a more friendly color theme. But I also did note some even prefer a more dark theme like Magnesium while others chose other color styles. In any case using the same color for font and background is a bug I did not note so far. You have a screenshot?
I also found visual bells and whistles to be rather balanced. For example KWin has lots of effect plugins but very few are enabled as default.
There are things which can and should be improved. No question there. Same applies for all projects, not only KDE. For paddings and margins mismatches look for example at http://www.sharpley.org.uk/node/23 and http://agateau.com/2010/12/27/common-user-interface-mistakes-in-kde... (two KDE hackers) and for ugly dialogs at http://techbase.kde.org/Projects/Usability/HIG/Dialogs (the KDE HIG for dialogs with sections like "Reduce the dialog flood" and "Dialog Layout"). Everybody is welcome to help to get that target done faster. Just join and contribute. Edited 2012-08-02 19:01 UTC