Those are the gold body morph. They are neat. My daughter had a golden-bodied, red-tail morph for several years. Wonderful, eye-catching tank.

They can cross and be backcrossed with the gray-bodied guppies to show that only one different chromosome is responsible. (They gray is dominent, so the fish needs both chromosomes to show gold. If you can get an inter-library loan of the Noburu Iwasaki book Guppies: Fancy Strains and How To Produce Them, he works that out and illustrates the process.

I have a strain of Endler's which began throwing golds. Basically an absence of black, with everything else there. Some of them are throwing albinos now. I'm wondering if two chromosomes are involved. The golds are more attractive than the albinos in my eyes.

Glad to hear that you are "going for the gold!" ;)