The quality or state of being fulvid; the degree to which something exhibits a yellowish-brown color.
From 'fulvid' plus the abstract noun-forming suffix '-ness,' which converts adjectives into nouns describing qualities or states.
Words ending in '-ness' are endlessly productive in English—you can take almost any adjective and add '-ness' to talk about the quality itself, which is why English speakers can describe virtually any abstract concept.
Complete word intelligence in one call. Free tier — 50 lookups/day.