The ornamental design for the magnetic paint cups, as shown and described.
FIG. 1 is a top perspective view of a magnetic paint cups, showing my new design;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a front side elevation view thereof; and,
FIG. 8 is a rear side elevation view thereof.
The broken lines showing a portion of the magnetic paint cups are for the purpose of illustrating environmental structure only and forms no part of the claimed design.