It can be very difficult to distinguish between torbie and tabby cats. For me, it may be almost impossible to be sure, on occasions. Ideally, you have to be a member of the cat fancy with some real experience. The difficulty depends on what type of tabby and torbie is being compared. Both are types of cat coat and not cat breeds, as you probably know.
Perhaps, the only certain difference between torbie and tabby is that torbie has some orange fur while the tabby does not.
It could be said that a torbie is a type of tabby cat because the coat is partly tabby and partly tortoiseshell (orange and black fur). The torbie is a mixture of the two types of cat coat. A straight tabby cat has a spotted, striped or blotched tabby coat (classic tabby). The torbie coat is orange and black in various patterns with some tabby added. The tabby coat can be in various colors and densities such as brown tabby and grey or silver tabby. Here are some pictures, which show the similarities between these types of coat because the comparison is between brown torbies and brown tabbies.
As I see it and as mentioned, the difficulty in distinguishing between torbie and tabby is when the tabby cat is a brown tabby and the torbie is a brown torbie. This is because the color brown is close to the color orange if the orange is dispersed throughout the coat or diluted. But if we are comparing a grey tabby with a torbie cat you’ll see a clearer difference between the grey of the tabby and the orange and black of the torbie.
Torbies are also called ‘patched tabbies’ because they are tabbies with patches of orange (red) or cream (diluted red, I believe).
There is a wide range of types of tabby and torbie cat coats. For example there are silver classic torbies or diluted versions of it. These variations make comparisons more complicated. Both cats have the M mark on the forehead.
Note: Despite it being a bit boring, I have consistently used the same photos by Helmi Flick to describe these cat coats. I do this to be sure that I illustrate the article correctly. It is tricky sometimes…Michael.