What reactions occur when mixing copper sulfate and sodium hydroxide?
As noted in your question and in one of the comments, copper forms many different complexes having a variety of colors from red to green to blue to black and probably more.  Of course the situation here is even more "complex" (sorry) as you can end up with mixtures of the different copper complexes, as appears to be the case over the course of your experiment.  

The formation of some cupric oxide ($\ce{CuO}$) would account for the appearance of an insoluble black precipitate.  This could happen from the decomposition of some of the $\ce{Cu(OH)2}$.  

$\ce{Cu(OH)2}$ itself should be a greenish to pale-blue insoluble precipitate.  

It is possible that the original $\ce{Cu(OH)2}$ precipitate appeared more blue than green due to the blue $\ce{CuSO4}$ solution.  As the reaction proceeded, $\ce{CuO}$ and more $\ce{Cu(OH)2}$ precipitated to give the black-green precipitate you observed.