The words are drawn from the British section of Google's Ngram database , meaning they are words which have appeared in books published in Great Britain. They therefore include proper nouns (Bessel, a German astronomer), foreign words ('ecoles'), and some words whose meaning is not immediately clear ('sallal').
When widening our search for hex codes with meaning, we made three substitutions: '1' for 'l', '5' for 's' and '0' for 'o', meaning that all the colours on Lexadecimal are those whose codes can be formed 6-letter words comprising the letters 'a', 'b', 'c', 'd', 'e', 'f', 'l', and 's'. Thanks again to Ben Griffiths, whose semantic web colours gave us the original idea. Meanings are from dictionary.com.