how do you tell the difference between male and female guppies?

Their anal fins are different shapes. The females can a anal fin that points down more and looks like a fin. The male has an anal fin that looks like a tube. This is called the gonopodium. Here is a website with a pic of the fins http://www.aquaticcommunity.com/aquariumforum/show... . This also applies to other live breeders.

Male guppies have a gonopodium for reproductive applications. it is a changed anal fin that seems rod formed, is hung on the point of the body and factors rearward in the route of the tail. that is used for transfering sperm to the female. as far as being gray it would properly be a count number of age, yet women usually have very bland colour, so more beneficial than likely they are women.

the females will be very grey and dull and the males tend to be very colourful. I know this due to keeping tropical fish myself especially breeding guppies.

Male guppies are penis carriers (outie) and female guppies are vagina carriers (innie).

depending if there butt holes are closer or farther