You can use this...some of it doesn't apply for glo-fish obviously since glo-fish will not have any black/blue skin...but some if it does still apply: http://www.zfic.org/Tutorials/Gender...on%20guide.pdf
And if they are big enough, you can try to locate the cloaca, only present on females...ZFIN View Publication:ZDB-PUB-091120-25
(go to the bottom of the page).
Out of all of the above though, the only thing helpful to me for sexing my Danios are the difference in belly size (females have big bellies) and the fish's activity and whether or not they are the ones doing the chasing (males) or the running (females).
My Danios are way too fast and small for me to try to locate the cloaca...and trying to determine whether or not the streaks are silver or yellow is also pretty hard and some of my danio have both silver and yellow streaks i think so that doesn't help me.