Christina,
This is an excellent question, and one not many people know the answers to. I'm not an expert, but I have researched it a little.
Most all Leopard geckos have some orange on their tail base. This is normal. True Carrot Tails, originated by Ray Hine, were created not only by selectively breeding for more orange on the tail base, but he imported a genetic hypo to put into the CT 'line'. This hypo is a very strong dominant/co-dominant gene that basically strips away all melanin from the geckos back, which is why you see most of the Carrot Tails are hypo or Super Hypo. Not all Tangerines are Hypo or Super Hypo.
That said, All Tangerines Are Not Created Equal. I could put the ugliest yellow/tan leopard gecko on the classifieds here and call it Tangerine. It's all in what I want to call the gecko. Before we had tangerines, we had this problem with what to call a High Yellow. Because it's sometimes difficult to capture true colors with a digital camera, it's easy for someone to unintentionally 'misrepresent' their gecko (look at Garrick DeMeyer's pictures; his geckos actually look better than the pics). Not only that, with blacklights or photo software, people can put a tint to their geckos to call them Tangerine. What this means is that the consumer has to be educated and needs to be able to trust their breeder, and know what a real tangerine should look like.
Many of the True Carrot Tails on the market are not even Tangerines. They are just plain yellow or high yellow. This is the reason you see so many Carrot Tail crosses, or offspring from Carrot Tail x Hypo Tangerine matings. It's not that people only had one carrot tail, it's an attempt to put more color into the geckos. Just look at some of Kelli Hammack's pictures in her photo gallery to see good examples of some of the crosses I'm talking about. I used to be of the impression that I had to have a True CT x CT baby, but then after getting my first '5 star' carrot tail, I realized that they are really lacking the orange that people expect from a Super Hypo Tangerine Carrot Tail.
Here's a picture of what I think you're looking for in a Tangerine with spots. Albey Scholl is the King of Tangerines, even though you'll find mostly Carrot Tails on his website right now. This boy came from Albey a couple years ago. His Tangerine is unmistakable; not a hypo, but a bright orange that has turned into a deep rust orange/red as he has grown up. You'll find that as geckos grow up, their colors change more into adulthood. My 'baldy' Carrot Tail has even started to grow a couple light brown spots on her head. This boy is 100g now. Albey really does have some awesome, healthy geckos. I'm happy to say, though, that the genes are still in there, he mated with a High Yellow girl this year and his babies are showing some tangerine highlights.

Here's a picture of three of my carrot tails. The youngster is a product of a HTxSHCTB cross, and that's her 'baldy' mom to the left. I think even in this dark picture, you can see the benefits of putting some real color into the CT line. It's subtle, but noticeable. If I keep the baby, I'll be able to further breed her to more tangerines to hopefully someday be able to turn out some of the colors Kelli's got in hers. *fingers crossed*

Lastly, check out this guy's colors. I don't think anyone could dispute the 'tangerine' label on him. I was talking about geckos with this contrasting color to them a while back with a guy and he remarked that it wasn't as nice as all over orange, but I think it's just as nice or nicer. At least you can tell even in bad pictures that you're getting a truely orange gecko. Once again, as he ages, his orange is turning from a vivid orange to a red/rusty coloration. He's the dad to my crosses this year.

Anyway, I hope that this has somehow helped, especially if you can read all the way through it and have it make sense. It's been a while since I had Eng101 
-----
Rob Jenkins
Have you seen the GeckoCam?
Buy Geckos Here
Email Me