Who could help me understand this : "But whereas the political salience of greenery has wilted, the government's environmental politics are holding up" ?
I would be delighted if I could help in this matter. Let me paraphrase the sentence:
Looking at the greenery and a green environment (in cities, for example) does not necessarily evoke political thoughts in people anymore as it was still some time ago (=the political salience of greenery has wilted) , that is, the mere sight of greenery in an urban environment is s not as much politically relevant anymore and is already somehow taken for granted. Nevertheless, environmental issues and aims are still an important issue for the government.
Imagine: Still some time ago, looking at the greenery in cities reminded the citizen that the local administration did a lot to improve the living conditions of their voters. But this effect has worn off over the time. Seeing trees, shrubberies and flower beds in the city is not as conspicuous (=salient) as it once was and has therefore not as much political relevance anymore. But that doesn't prevent the administration from still putting environmental on their agenda. (='They still hold up environmental politics'). That's speaks for the government.
P.S: or let me put it more succinctly:
'Planting trees in the city doesn't bring voters anymore, but the government hasn't noticed it yet.'
Thanks very much, it helps a lot and it is perfectly well in touch with the topic named "a lighter shade of green"