The relevant section of the walk through does refer to "...a red Action card, or a red Spell card,..." and the Spells that require red Mana are tinted red (well the backgrounds to the text are anyway) so I'd assume that they are included.
Where is the relevant part of the walkthrough? I went digging for it and couldn't find that line. The closest I found was under "Revealing a Mage Tower" (p14), in discussing enemy resistances and resistance to special effects. But I didn't see anything about spell cards.