The Kid Made Modern folks decoupaged a real pumpkin for this geometric pumpkin tutorial, but to preserve your work, a foam pumpkin would be the way to go. It would also be a great way to make those faux ones look less, well, foamy. Supplies are minimal and include what you see above: colored tissue papers, scissors, a paint brush, white glue OR matte decoupage medium, and, of course, a pumpkin.
Seeing this done with a white pumpkin makes me wonder what could be done with an orange one. Perhaps using in black and white tissue paper? For the entire tutorial, visit Kid Made Modern.
Pumpkin Pattern Parade [Kid Made Modern]