I’m usually the one who’s mystified by grammar, but this one seemed quite straightforward to me for some reason.
My understanding:
<descriptive-noun-phrase> の <noun> is a really common construct in spoken Japanese：
汚いレストラン
レストランは汚い
床が汚いレストラン
汚い床のレストラン
I believe all are grammatically correct and mean roughly the same thing, but the latter two zero in on the floor being what’s specifically dirty.
I’d diagram the senryu like this:
That is, the descriptive noun phrase here is 「サンプルが腐った色だ」 but because this is used as a modifier for レストラン rather than a standalone sentence, the だ gets replaced with の.
Any corrections to my understanding? This is what I assumed from my first reading.
Edit: I forgot to link to a thread related to this: Confusion regarding の in Word Use Examples