From The Collaborative International Dictionary of English v.0.48 :
Mottle \Mot"tle\, v. t. [imp. & p. p. Mottled; p. pr. & vb. n.
Mottling.] [From Mottled.]
To mark with spots of different color, or shades of color, as
if stained; to spot; to maculate.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 :
mottling \mottling\ n.
1. the act of coloring with areas of different shades.
[WordNet 1.5]
2. A mottled pattern.
[PJC]
From WordNet (r) 3.0 (2006) :
mottling
n 1: the act of coloring with areas of different shades