The ornamental design for a foldingcolander, as shown and described.
FIG. 1 is a perspective view of the colander showing my new design, the broken lines are for illustrative purposes only and form no part of the claimed design;
FIG. 2 is a left side view thereof, the opposite side being a mirror image;
FIG. 3 is a front view thereof, the opposite side being a mirror image; and,