You could also put on some eyes and a nose if you felt so inclined; I've decided to leave it as it is for now until I'm bored and then I may add more bits and pieces. I think it' super cute as it is :-)
For the ears you'll need to follow this simple pattern.
EARS (Make 2, unless you're a freak cat!)
Cast on 14 sts in your main colour - in my case black.
St-st 10 rows
Ssk, k10, k2tog - 12
Purl row
Ssk, k8, K2tog - 10
Purl row
Ssk, k6, k2tog - 8
Purl row
Ssk, k4, k2tog 6
Purl row
Ssk, k2, k2tog -4
Purl row
Ssk, k2tog -2
B&T tightly
Now with a groovy pink for the inner ear make 2 of the following:
Cast on 10
St-st 8 rows
Ssk, k6, k2tog -8
Purl row
Ssk, k4, k2tog -6
Purl row
Ssk, k2, k2tog -4
Purl row
Ssk, k2tog -2
B&T Tightly.
Now you have to sew one black piece to one pink.
Place a pink section on top of a black one with the right sides facing each other and oversew around the row edges making sure that the cast on edges stay in line and do not get oversewn - this is where we shall add stuffing. You will find that when you turn this inside out you will have the excess black around the edge of the pink creating a border around the top and sides of the ear.
Add a little stuffing and then place where you'd like on the hat. I put mine quite far back as they seemed to sit better, but it's really up to you. You're best bet is to put the hat on and look in a mirror; try holding the ears in different positions until you like what you see and then pin them down carefuly. Remove the hat and sew the ears down permanently.
Now... doesn't that look the cat's whiskers?! MEOW!!!