Masking Tape

Masking tape works on eggs, too.  The edges will be a little fuzzier than electrical tape, but it depends on what look you are going for (and, often what you happen to have around the house).  This example is pretty tame, but you can cut out letters, shapes, and more.  I once did a landscape image on an egg with different "layers" of mountains and such.  You have to really think backwards - but it works!