Uncited general claims followed by cited specific claims – is this an accepted writing style?
Certainly general statements that are common knowledge do not require citation.  Particularly if the general claims just help to provide a framework for thinking about things (context), are reasonable, and are not truly needed for the paper.  

However, different people have different opinions about what is common knowledge, or is reasonable, or is important (say in putting the work in context), and part of your job as a reviewer is to point out where you think citations should be added or assertions should be questioned.  The authors always have the option to disagree, but at least if you make a suggestion, they should think more carefully about the validity and evidence for such an assertion.  (cf. my answer https://academia.stackexchange.com/a/66329/19607)

In your example, you might ask for evidence that they "appear green to most people and animals," or just point out (politely) that that's a stupid statment.

As another example, here's something I wouldn't expect a reference for:


  The only known techniques to attack Problem A are Method X and Method Y.  Method X was pioneered in [cite 1] and Method Y was recently applied in [cite 2].


It's hard to give a reference for the first assertion, and maybe the reviewer will be aware of a Method Z and can point it out.  Or maybe there is a Method Z but it got neglected by the authors and the referees.  Or maybe the referee's not sure.  This is why some people might prefer to be more modest and say "The only techniques we are aware of..." but people write in both ways, and as a referee I wouldn't say anything unless I actually thought the authors were neglecting something.