Yellow - Exceptional
Green - German Words
Blue - plural animals identical to their singular forms
Purple - plural words that are very different from their singular forms 

Continue for full spoilers 
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Remarkable singular special unique 
Angst die kinder wurst
Dear shrimp sheep squid 
Dice lice mice oxen 

Have a great day

I thought dice-mice-lice was an obvious trap, because dice can be both the singular and plural and fit better with “plural the same as singular”. Of course the pedants at the NYT see die-dice as the official pair. But what really got me was squid-sheep-deer-shrimp. It’s not 2 squids, 2 sheeps (okay, I knew this one), 2 deers, 2 shrimps?

I’m not a huge fan of the official description for purple though. “Very different from their singular forms”? Oxen is literally just “ox” plus “en”. It’s not modifying the singular form at all, just adding something to the end, the same way many words add “s” or “es”. Even “dice” is kinda just “die” plus “s”, with a twist.

I thought of purple as just “plural words made without adding an ‘s’ to the end”.