Phlegm can have different colors.
You feel absolute pleasure when you get rid of a chunk of nasty phlegm in your throat. It’s similar to a good defecation experience. But people are more familiar with defecation, so diluting the pleasure.
There was a joke that’s been impressing me since I was a kid.
Two guys walk into a theater, they see a spittoon in the corner. So they make a bet, the one with the courage to take a bite of the phlegm in the spittoon gets a free movie ticket from the other one. So one guy lifts the spittoon and starts drinking it. After a while, finally puts him the spittoon down. The other guy looks into the spittoon, it’s empty without a tiny bit of phlegm. “Why did you eat all of it? Only a single bite is enough!", he asked. “It is so thick, homogeneous and together, I couldn’t cut it with my teeth, so I had to swallow it altogether!”