Disenchantment was the first thing that popped into my head. For a Matt Groening animated series, the colors are incredibly dull. The humor and overall story also left me disappointed.
You cod say, it left you disenchanted
Oh damn and the name has been there all this time.
Interesting. Doesn't just change the colour - the woman in the headdress also loses her smile.
Horribly dirty isn't realistic either though. People washed their clothes and hands and went to bathhouses. https://www.worldhistory.org/Medieval_Hygiene/