Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
helvus, a, um, adj. [perh. a weakened form of gilvus, yellow], light bay: color vaccarum, Varr. R. R. 2, 5, 9; cf.: color boum, qui est inter rufum et album, appellatur helvus, Paul. ex Fest. s. v. ‡ helvacea, p. 99 Müll.