Your shirt is of the same colour as John's.
 Your shirt is the same colour as John's.
Yes,  and  have the same meaning, but NPs cannot be adjectival, as I explained to you in comments.
In  the NP "the same colour" is complement of the prep "of", and the whole PP "of the same colour ..." is complement of "be".
In  the NP "the same colour ..." is subjective predicative complement of "be".
The crucial points are that predicatives may be AdjPs or NPs, and they are not modifiers of the subject or object, but complements of the verb:
 The house was white. [AdjP as subjective PC of "be"]
 We painted the house white. [AdjP As objective PC of "paint"]
 Ed was a teacher. [NP As subjective PC of "be"]
 They elected him treasurer. [NP as objective PC of "elect"]
We refer to the PCs in  and  as subjective (or subject-oriented), and those in  and  as objective (or object-oriented). Importantly, in all cases the PC is complement of the verb, not the subject or object.
Note that it is important not to conflate the terms word class and function. NPs and AdjPs are the corresponding phrasal categories of the word classes adjectives and nouns. By contrast, complement and modifier are functions.
EDIT: I don't use the terms 'predicate adjective' and 'predicate noun', as it's obvious whether a PC is an adjective or a noun. But for those who do use those terms, where the PC is an adjective it can be called a predicate adjective (or AdjP) and where the PC is a noun (or NP) it can be called a predicate nominative:
 Ed seems nice. [predicate adjective subj complement]
 Ed is a teacher. [predicate nominative subj complement]
Importantly, although the adjective "nice" and the noun phrase "a teacher" both refer to the subject, their function is complement of "seem" / "be".