A colored device casing includes a base, a color layer and a bonding layer. The base has at least one smooth region. The bonding layer is positioned between the base and the color layer and bonds the base and the color layer together. The color layer includes at least one metal layer. Portion of the color layer corresponding to and located over the smooth region has a value of L* in a range from about 81.59 to about 83.59, a value of a* in a range from about −0.55 to about 0.45 and a value of b* in a range from about −0.60 to about 0.40 according to the Commission Internationale del'Eclairage LAB system. A surface-treating method for fabricating the colored casing is also provided.