We claim the ornamental design for a decorative light cover, as shown and described.
FIG. 1 is a perspective view of a decorative light cover,
FIG. 2 is a front elevational view of the decorative light cover,
FIG. 3 is a rear elevational view of the decorative light cover,
FIG. 4 is a left side elevational view of the decorative light cover,
FIG. 5 is a right side elevational view of the decorative light cover,
FIG. 6 is a top plan view of the decorative light cover; and,
FIG. 7 is a bottom plan view of the decorative light cover.
The broken lines shown in the drawings are included for the purpose of illustrating portions of the decorative light cover, and form no part of the claimed design.