From The Collaborative International Dictionary of English v.0.48 :
Yellow \Yel"low\, v. t. [imp. & p. p. Yellowed; p. pr. & vb. n. Yellowing.] To make yellow; to cause to have a yellow tinge or color; to dye yellow. [1913 Webster]From WordNet (r) 3.0 (2006) :
yellowed adj 1: changed to a yellowish color by age; "yellowed parchment" [syn: yellow, yellowed]