The element of the Knives is Air and the colour is Yellow. The Knives suit is about intellectual clarity, consciousness and perception.
There are again 10 yellow roses in the Ace, one for each card. The books says there is one rose for every following number cards to symbolise that they are all contained within the Ace. Yellow roses stand for joy and security, friendships, clarity, truth and intellect. Yellow/gold is also traditionally a symbol of corn (and coins) and therefore it stands for prosperity, security and stability. The Wheel of Fortune has one yellow rose but other than that I only see a few yellow roses in the Four of Knives. (And even those look more cream coloured than pure yellow.)
I´m not sure what the yellow stones on the knife are. I´ve been thinking they might be amber but they could equally well be some other valuable stone or just polished gold. The only Vampyre who wears same kind of stones is the blindfolded lady in the Two. She has a fabulous ring and the stone looks opaque and very much like amber.
The animal of this suit is the Raven. There are Ravens in the Three, Six, Prince and Queen of Knives. There is also a Raven in the World and some in the Fool. But instead of ravens there seem to be several other very interesting looking winged creatures in the Knives suit. The black angel in the Five looks to me like she is protecting the sleeping girl (-but I remember some people saying that it looks threatening). Another winged angel can be seen in the Seven. I think she looks more lost than threatening or dangerous. The Daughter of Knives has got feathers on her back which could be just her fashion garment but it could equally well be her wings. The Stone angel in the Four is interesting. I´m not sure if the raven next to her is dead or alive but there is blood around it.
Some interpretations for this card
(most from the companion book for this deck):
-clarity, justice, truth is revealed
-learning, studying, planting seeds of thought
-swift changes, decisions
-cutting through confusion and entanglement with clean incision
-control, force, being firm
-purity, health, healthy lifestyle, exercise