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]