If your blue delta females are pretty impressive specimens and you like the strain, you may want to stay with blue delta males. If you do a Google image search for blue delta guppies, you will get a few shots of nice blue deltas. (Curiously if you do an image search for blue delta guppy, you will get a lot more hits, several of which are NOT blue deltas! They are simply photos on the same sites.)

I would certainly let them drop first before doing anything else about breeding! Raising them on the side, if you have space, would keep that strain as it is. Depending upon whose blue deltas those are, they could be good trade material and/or possible sales/swap material, if you have a nearby independent fish shop.

By the way, once in a while, blues will throw purples or greens. That is kind of a neat surprise. Some guppy breeders will keep related lines of blues, greens and purples and even back cross them from time to time. (Line breeding is an important subject in itself. Your handle/signature suggests you may already be familiar with that.)

As you probably know, it takes a breeder a long time to "fix" a nice strain so that it breeds large delta tails with consistent, strong colors. While experienced breeders will sometimes cross a blue delta into their strain of blue deltas to keep sizes large, even there they may have to be especially selective for a couple of generations to get consistently large and color consistent offspring.

So if you want to continue that strain, stay within that group for breeding. On the other hand, a lot of hobbyists enjoy crossing different guppies to see what will be produced. It will take a couple of months to really see what came about. If that is what you want to do, go for it.

If you Google "line breeding" or guppy crosses, one will also get some material. We haven't done much specific predicting on GL. Often pet shop guppies have mated with quite a collection of males. Sometimes their genealogy is pretty mixed too.

One of the nice things about "playing" with guppies is that if a female is mated with a male and you don't like the colors (or other characteristics) of their fry, you can set up that female to mate with another specific male right after she drops fry (that day or the next or it may be too late). Most of the fry in the next batch will descend from that later male.

A great book on the subject is Stan Shubel's THE PROPER CARE OF GUPPIES (TFH Publications, 1995). It is out of print, but your public library could probably get it for you via inter-library loan. Copies for sale on-line are now often terrifically expensive, though once in a while a reasonably priced copy is offered. (That's how I got mine, though I felt a little sleazy, since it was a sale at www.seahorses.com of a collection by a really genuine and gracious aquarist who had passed away)

A few sites to browse for images, just for fun:

http://www.tropicalfishintl.com/guppy.htm

http://www.ne.jp/asahi/medaka-ken/k.t/framepage5.html

http://www.world-guppy.de/

http://www.laurellakeguppies.com/

http://www.ifga.org/

http://www.deltaguppies.com/

http://www.arihood.com/azgenetics/guppycolors1.html

http://www.ne.jp/asahi/medaka-ken/k.t/framepage5.html

http://www.ifga.org/guppy_store/gs_roebuck.htm

http://www.guppy-art.de/galerie01.htm

http://www.imagestation.com/album/?id=4288225435

http://www.imagestation.com/album/index.html?id=4287485191