Following figure exemplarily shows parts to compare.
The figures show standard settings:
1. Part blue
2. Part red
Result yellow
Difference 1-2
Difference: Part 1 minus part 2
Difference 2-1
Difference: Part 2 minus part 1
Smaller part (which is completely contained in the larger one) minus larger part results in nothing = no yellow coloring
Symmetric difference
Sum of differences between part 1 and part 2
Union minus intersection
Shows areas where parts differ.
Intersection
Shows areas where parts are identic.