The ornamental design for a grilleaccenttoppanel, as shown and described.
FIG. 1 is a perspective view of a grille accent top panel showing our new design in the environment of a vehicle;
FIG. 2 is a front perspective view of the grille accent top panel shown in FIG. 1;
FIG. 3 is a front view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The broken lines shown in FIG. 1 illustrate environmental subject matter that forms no part of the claimed design. The broken lines in FIGS. 2-6 illustrate portions of the grille accent top panel that form no part of the claimed design.