joined a Facebook group for Connections and looking at some of the posts confirmed that the colors do seem to designate what is perceived to be easiest to hardest which follow the spectrum ...
"Spelt and spelled are two different spellings of the past tense of the verb βspell.β The spelling tends to vary based on the version of English you're using: In US English, βspelledβ is standard. In UK English, both βspelledβ and βspeltβ are acceptable."