According to Wiktionary, Polish czarny is from PSl *čьrnъ, and czervony is from *čьrvenъ. At least prima facie the soft yers appears to have become different vowels in Polish.
I'm aware of the following sound rules (from Wikipedia):
- PSl ě becomes a before unpalatized alveolars; e becomes o.
- Strong yers in PSl become e
The rules kind of explain czarny and czervony, but not quite. At least according to the rule, a soft yer does not become ě, and rv in *čьrvenъ is not quite palatized (are they)?
How can the modern czarny and czervony be explained?