From Four Flies on Grey Velvet through to Suspiria there is a progressive shift in colour. In Four Flies colour is still something which tends to inhere in objects, things or images: This curtain is red; the lining of this (fetishistic) box containing a syringe is red; this liquid drawn up into the syringe is blue. In Deep Red colours begin to become independent: While the reds of the opera house still inhere in objects, the blues and oranges of the burning house of the screaming child, as they play on Gianna’s form, are independent. Finally, in Suspiria colours break free. They are in themselves, no longer subordinate to objects. One moment a scene is bathed in red, another blue or green, without commentary from those diegetically engulfed. Colour here, and in Inferno, is pure intensity.
(cf. The impulse image in Bava, in Sam Ishii-Gonzales's Deleuzean reading http://archive.sensesofcinema.com/contents/directors/04/bava.html)