The ornamental design for a diaper having colored back ears, as shown and described.
The sole FIGURE is a plan view of a diaper having colored back ears embodying the new design.
The ears and fasteners shown in the figure are flat and co-planar, and any side or reverse surfaces form no part of the claim. The broken lines in the figure illustrate portions of the diaper that form no part of the claimed design. The grayscale is included to indicate color.