Oh my--she's lovely Andrea!!! Gabby is actually a Torbie. She's 1/2 orange tabby and half grey tabby.
Bonnie, your girl is a Tortie.
She has one copy of an orange gene instead of two. She's not a Torbie, which I believe (not sure.. I could be totally wrong.. google something like "genetics" "torbie") requires an extra X chromosome.
The basic run-through of tortie genetics is this.. (you can get way more in depth articles and diagrams by googling "cat genetics" "tortie")
Female cats must have TWO copies of a gene (I think it's O, that's what I'm calling it anyway) to become an orange tabby (of any pattern) because it is on a different locus than other tabby colors (once again, of any pattern--i.e. classic, mackerel, etc, it doesn't matter). The O gene is ONLY found on the X chromosome, so if male cats have one copy of it they will be orange tabbies. Females need TWO copies of the O gene to become orange tabbies b/c they have two X chromosomes. If females only inherit ONE copy of the O gene, they will become torties (essentially they are half orange, and their base color shows through. As I said above, I'm not sure about the second chromosome thing, the cats could just have tabby coloring as their base coat).
Calico and Tortie differ in one way... Calicos have patches of [color--usually black] plus patches of orange tabby pattern on white. Torties may have white on them, even large amounts, but I don't think it's the same. I haven't found a truly good explanation for this.
I have one tortie girlie who is the love of my life.
I'll upload some pictures soon and add them to the thread, as well as a few of my neighbor's kitty, Megan, who is a chocolate tortoiseshell point with white.