I'm planning to use 3x of those [drivers] for each color (RGB) and use Arduino to control drivers via PWM.
You'll only need one of those drivers per color. 3*1W as in 3 x 1W = 3W.
Keep in mind that VDIM_H is 2.5V and the Arduino's PWM is 5V. I've used the Arduino to control a PT4115 by using a voltage divider between the Arduino's PWM outputs and the 4115's DIM input.
Sorry, I explained it wrong. You're right. 3 drivers per 1 RGB-led - one driver per color.
I've looked PT4115 datasheet, and VDIM max voltage is ~6V. So voltage divider isn't necessary IMO.