The Matrix is a film in which a random office worker discovers that the entirety of reality is a mocking simulation created by dickhead robots and that his entire life is a lie. A twist that is subtly alluded to through the entire movie via the the strategic use of a of more green goo than an episode of a kid’s show in the 1990’s.
To explain, according to Matrix series costume designer Kym Barrett there was a pretty basic rule they adhered to throughout production when dressing scenes and characters, that the colour blue does not exist inside the Matrix. To this end every scene in the film set inside of the titular Matrix is tinted green, a motif that is admittedly hard to notice when you’re watching Carrie-Anne Moss side-kick police officers skull through a concrete wall in the tightest pair of pants imaginable.
Likewise, scenes set outside of the Matrix are generally tinted blue giving them a distinct look that is further emphasised by the film’s camera work. Specifically it’s noted that the Wachowski’s filmed scenes set outside the Matrix using longer lenses which drew a sharper distinction between the actors in them and the background and did the opposite for scenes set inside the Matrix. A level of detail that seems excessive given how obvious this distinction is due to the colour scheme but whatever.
Anyway, while you’d assume this would have been accomplished in post production, the effect was largely realised using practical effects. For example, the lighting for each scene was tinted either blue or green based on whether or not it was set inside the Matrix. However its what the aforementioned Bassett did that’s most ridiculous.
You see, according to Bassett she was so keen to adhere to the idea of reality being blue and the Matrix being green that every item of clothing worn by an actor for a scene set in the Matrix was dyed green. Which probably sounds unbelievable because there are literally characters in the film whose whole thing is wearing immaculately pressed suits and white shirts that absolutely do not look green, let alone like they’ve been rubbed against Shrek’s balls for half an hour. 
Well believe it or not those shirts are green, it’s just that they were cleaned so much that almost all of the green dye applied to them was washed away, giving them an almost imperceptible green tint that adds to the sickly green tinge each scene has. The same is true of all the black and grey outfits too, all of which were put through a green wash and then cleaned so that only the faintest whiff of green was left behind.
Hell, Bassett even got a company to custom print the material for Morpheus’ coat only to wash most of the dye off so that the effect was more subtle. A descriptor we can’t believe we’re using for a guy who headbutts his way through a concrete wall while screaming.
A fact that it makes it kind of hilarious that all of this subtlety was shat on from orbit when they re-released the movie and just put an obnoxious green filter over every scene in post-production. A change so bad they corrected it in another re-re-released we’re kind of pissed off they didn’t call The Matrix – Re-Reloaded.
