Additional: Blazons mostly concern themselves with the distinguishing element, the coat of arms on the escutcheon, with the external devices described mostly by reference – the papal tiara, an Earl’s coronet, a naval crown, etc. Mostly because in the heraldry of a European country these coronets were somewhat standardised – “everybody” knows that a duke’s coronet has acanthus/strawberry leaves – and for well-known crowns of sovereigns like the St. Edwards/Tudor crown, the Crown of St. Stephen, the Holy Roman Emperors Crown and of course the Papal Tiara developed over time well known depictions after their real likeness.
Pius XI didn’t bother to specify the tiara (the “triregnum”) in writing.
> La bandiera della Città del Vaticano è costituita da due campi divisi verticalmente, uno giallo aderente all'asta e l'altro bianco, e porta in questo ultimo la tiara colle chiavi, il tutto come al modello, che forma l'allegato A alla presente legge.
> Lo stemma è costituito dalla tiara colle chiavi, come al modello che forma l'allegato B alla presente legge.
> Il sigillo porta nel centro la tiara colle chiavi ed intorno le parole « Stato della Città del Vaticano », come al modello che forma l'allegato C alla presente legge.
Translated by Google:
> The flag of the Vatican City is made up of two vertically divided fields, one yellow adhering to the hoist and the other white, and in the latter bears the tiara with the keys, all as in the model, which forms attachment A to this law.
> The coat of arms consists of the tiara with the keys, as in the model which forms annex B to this law.
> The seal bears in the center the tiara with the keys and around the words "State of the Vatican City", as in the model which forms annex C to the present law.
From [1] – where the models in the annexes are printed in black and white.
[1] https://web.archive.org/web/20131217230421/http://www.unirom...
Getting pixel-perfect representations from textual descriptions seems like a fool’s errand. The original sin, of course, was depicting the coat of arms on the flag, although that seems to be long practice for the preceding flags of the Papal States and institutions, as seen in the linked digital book on Vatican Flags [2] in the article, which features a multitude of different ancient depictions of the flag, often displaying the Papal Tiara’s inner lining in … red.
[2] https://nava.org/raven-volume-25
(Edit: fixed quote formatting)