8 LED Chaser with 3 stage dimming LED output... lost where to start!

As part of a project I've been working on for some time I'm wanting to create a circular LED chaser which just travels around the circle. I've already created a basic shield for this (https://www.youtube.com/watch?v=DRk_6ZaD2lg) using shift registers but I would like to create the same thing but with a dimming LED effect as follows:

Although the image shows blue to purple, the lighter colours show the LED varied output, 100%, 60%, 30%.

That shows the first 6 steps but the idea is for it to be a continued cycle around the circle.

I need some pointers on how I go about it as I don't know anything about how best to go about the dimming. My ideal once I get this working on a Arduino is to shrink it to a Attiny84/85.

Anyone got any suggestions?

The first thing to consider is how many PWM pins are you going to need to control 8 LEDs.

Once you have the 8 pins defined, its a simple matter of setting the appropriate pins to the appropriate PWM levels.

My ideal once I get this working on a Arduino is to shrink it to a Attiny84/85.

It sucks when ideals clash with reality.