Lewis & Short

1. lūtum, i, n.,

  1. I. a plant used in dyeing yellow, yellow-weed. dyer’s-weed, weld: jam croceo mutabit vellera luto, Verg. E. 4, 44; Plin. 33, 5, 26, § 87; Vitr. 7, 14.
  2. II. Transf., a yellow color, yellow, Verg. Cir. 316: nimius luto corpora tingit amor, Tib. 1, 9 (8), 52 Heyne ad loc.