Quantitative differences in hue or softness! What a cop out. Red and yellow most certainly exclude each other. I.e. you can't have two colors in the same space. They are "qualitatively" different.
In any case, what is considered "qualitatively" or "quantitatively" different depends largely on what aspects of the thing are being considered. For example, dialecticians like to talk about the change of water into ice as a "qualitative" change (referring, of course, to hardness!). From another perspective it is not a qualitative change since in both cases the substance is h2o. Or, to take my example, mashed potatoes and regular potatoes may seem to be merely "quantitatively" different from one perspective, but try throwing them at your friends' head -- they will be aware of a very qualitative difference.
). The "contradictions" that Marx speaks of are not logical contradictions, though they can be misdescribed by paradoxes (which are logical contradictions), which Marx sometimes does purposefully so as to point out inconsistencies in political economy, or to justify his own course of argument.
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Big fan of Zizek's take on it, which is basically that the subject both arises from and is the split between the subject and object, or in Butler's terms,
This is a situation where I think talk of a dialectic is spot on.