The basis principle is simple: female praying mantises have 6 abdominal segments while males have 8. The final segment of the female is much larger than the others while the male has several small segments towards the end of the abdomen. If you have to count the segments, you should look at the underside of the mantis. You can't tell by color or wing length unless you know which species you're looking at and one species of mantis can have multiple colors too.