And with her pale skin and dark hair offset with often vivid lip colours and slickly outlined eyes, Katy has quickly mastered the retro glamour of the most memorable Hollywood era.
But it's Katy's hairstyle that sets off this outfit to give her daring silhouette a sophisticated finish.
Katy's hair has been set on large heated rollers. Start by winding the hair in large sections - to create big waves of movement - from the ends upwards, with each section of hair on the outside so that hair curls under.
Carry on winding up to the root and pin into place to allow hair to set as it cools.
Around the front, twist sections once or twice as you wind to create the kinks that frame the face.
Once all of the hair has cooled, unwind and brush through gently with a cushion-backed brush which smoothes the hair in sections without breaking up the wave.
Use a tiny amount of gel mixed with hairspray around the forehead to create a little height and push hair back from the face.
Smooth serum over the surface of the hair for shine, and finish with hairspray for more shine and hold.