Absolutely not. There's no clear, ambiguous definition of "species" that does not have counter-intuitive implications. No, the classic "fertile over two generation" thing you learn in high school doesn't cut it. Also, the commonly used criterion vary from which domain is being dealt with.
In practice, this means that two individuals are said to belong to a different (resp. identical) species if everyone in the community agrees that they do. That's what it means to be a "social construct", not that the differences per se aren't real.
Justifying other statements on the lines of "X is a social construct" similarly, where X ranges across a variety of more-or-less controversial concepts, is left as an exercise to the reader.
#0000ff doesn't exist in nature. Human beings don't see color directly in hexadecimal values - indeed, additive color (RGB) as broadcast from a monitor and subtractive color as exists in nature are physically different processes. Rather, the perception of color is subjective and error prone (see a HN subthread on the color brown[0,1] or other examples of color illusions like the viral dress from a few years ago, or the red-grey illusion[2].
Blue is a social construct because what "blue" means is taught to us by the culture around us, and different cultures classify colors differently[3,4]. If one culture considers blue and green to be the same color, and another considers them distinct, that's not merely a disagreement over taxonomy, but concept.
