Hrmm...actually, the only real information on the Cathay comes from a RP dev interview, with employees that are still there. The only info is that they're bigger and stronger than the Suthay-Raht.
So................I guess it's still left in the air of what their fur pattern is! http://www.imperial-library.info/content/interviews-3-booksellers.
Here is the relevant part:
Jobasha:
Ah, you are wiser than most, for the only Khajiit most men notice are the Ohmes-raht and Suthay-raht.
Khajiit are bound to the Lunar Lattice, the ja'Kha'jay. The phases of Masser and Secunda at birth determine the form a Khajiit takes in life. Khajiti newborns look very similar to one another, with their form becoming clear over several weeks. We are smaller than you humans when we are born, but we grow faster.
When Masser is new and Secunda is full, the Ohmes is born. They are like the Bosmer, but sometimes shorter. Many Ohmes tattoo their faces to show they are Khajiit.
When Masser is new and Secunda is waxing, the Ohmes-raht is born. They have light fur and a tail, but they walk on their heels like men, and can be mistaken for men at a distance.
When Masser and Secunda are new, the Suthay is born. They look similar to Jobasha, but smaller.
When Masser is new and Secunda is waning, the Suthay-raht is born. Jobasha is a Suthay-raht, as are nearly all Khajiit in Morrowind. Other races call the Suthay-raht "Ja'Khajiit," but Jobasha knows not why. "Ja'Khajiit" is one of our words for Mehrunes Dagon.
When Masser is waxing and Secunda is full, the Cathay is born. They are larger than Jobasha, and stronger.
When Masser and Secunda are waxing, the Cathay-raht is born. They are even larger and stronger than the Cathay.
When Masser is waxing and Secunda is new, the Tojay is born.
When Masser is waxing and Secunda is waning, the Tojay-raht is born.
When Masser is waning and Secunda is full, the Alfiq is born. The Alfiq is like what you would call a "housecat." Jobasha does not advise calling an Alfiq a "housecat," for while they are not made to speak your language, they do understand it.
When Masser is waning and Secunda is waxing, the Alfiq-raht is born.
When Masser is waning and Secunda is new, the Dagi is born.
When Masser and Secunda are waning, the Dagi-raht is born.
When Masser and Secunda are full, the Senche is born. The Senche is very large, but similar to the Pahmar-raht. They stand as tall as an Altmer, and can weigh as much as twenty Altmer. Other Khajiit ride them.
When Masser is full and Secunda is waxing, the Senche-raht is born. The Senche-raht is much larger and slower than the Senche. Their legs are straighter and their body is not as long. They stand as tall as two Altmer and can weigh more than fifty Altmer. These are also ridden, especially in battle. Imperials call them "Battlecats," but again, Jobasha does not suggest calling a Senche-raht a "Battlecat."
When Masser is full and Secunda is new, the Pahmar is born. They are like what you would call a "tiger."
When Masser is full and Secunda is waning, the Pahmar-raht is born. They are like the Pahmar, but larger and more dangerous.