Have a look here: Wikipedia: Italian heraldic crowns.
I looked, and I really don't know what to say...Royal Decree of Jenuary 1st 1890 clearly said: "Le corone del Re, della Regina e del Principe Reale ereditario sono foderate di un t˛cco di velluto chermisino
" (King, Queen, and Royal hereditary Princes's crown are all lined by a crimson velvet toque
). So wikipedia's picture is just wrong.
: To make red you need some very rare, exotic insects or huge amounts of very rare plants
That's exactly why red was considered a king's colour
; red fabrics were very very expensive (let's think that ancient Phoenicians based a large part of their economy on the trade of red fabrics; they used a mollusk called murix in order to get a precious purple dye) and so only powerful and rich people could get them, such as kings, emperors, noblemen, etc...Roman Senators, for istance, wore red-hemmed white robes as a sign of their high rank.
What is your opinion about the coronets for the Savoy-Aostas and Savoy-Genovas?
Savoy-Aosta's croronet looks right, but Savoy-Genova's one looks totally wrong while it should look like Savoy-Aosta's one. The Royal Decree on Jenuary 1st 1890 said: "La corona dei Principi Reali Ŕ chiusa da un semicerchio d'oro, movente dalle foglie laterali, fregiato superiormente con una fila di piccole perle, tutte eguali; e cimata dal globo, cerchiato e crociato, eguale a quello della corona del Principe Reale ereditario
." (Royal Princes's crown is closed by a golden half-circle, superiorly decoreted by identical little pearls; it's headed by a globe - wich's decoreted by a circle and a cross - wich's identical to Royal hereditary Prince's one.
). The Royal Decree had also a sketch of every coat of arms: Savoy-Aostas' coat of arms Savoy-Genovas' coat of arms
The coronet wich appears on wikipedia.com could be a simple not-royal prince's coronet; unlike UK, in Italy the rank of Prince was allowed also to not-royal families, such as Colonna family in Rome, or Capece Minutolo family in Naples, or Borromeo falily in Milan...the heads of these Houses still are Princes, but of course they're not House of Savoy's members.