anal fins on males pointed and round on female, thats how you tell most livebearers, oh and most female guppes wont have coloring to head from the tail, most of it stops at the middle of the body or just on the tail
If you are trying to sex fancy guppies. Its pretty easy, the male will have a fancy tail with lot of color and the female belly is usually bigger then the male and have less color.
With all of the special breeding of guppies, females are becoming more colorful and 'flowey' like the males. To really tell, you have to look at their anal fins.
Pictures are worth a thousand words: male is circled, female squared. (not my pict.)