“Its better to try and fail than to never know and always wonder” remember that quote?
Have you gone to guppy shows and wondered how those beautiful guppies were produced and for a moment thought if only I could? That’s one of the one reasons why should try crosses and outcrosses in guppies
Few reasons why a cross would be the best bet
Your color strain has become weak and needs a compatible cross to improve
Your fish lacks color, size, lost vigor, then you need a cross
Crosses produce fish with hybrid vigor and some of the go on to win shows
Most importantly you will learn by doing crosses, otherwise you will never know your fish completely, but as with other things, before you start crossing you need to know few things about what colors are compatible and will produce the desired outcome.
I am going to limit from my experience here, some of the crosses I have carried out in my fish room are HB purples with purples, HB Blues with blues, HB purples with HB blues, Reds to HB reds, HB blues to Greens and vice versa in some cases. I would say, most of the crosses worked out good, some very good and some produced winning fish, overall I learnt a lot in the process like understanding where HB gene is present, is it in male or in female with my lines, which color is dominant and which is recessive and which crosses are to keep and which ones to dump. This helped me to get some recipes for success, fish always had great vigor.
Below is a cross which resulted from crossing a HB purple with purple, I had to do this cross because my line of HB purples were getting too dark and I need a line to lighten the purple on my HB purples
Below is sample example of purple line which was used
Guppies by Raj Seshagiri 