RGB LED PWM colors "pulsate"

I'm using an Arduino Megao to create a project with color LEDs and I'm finding some problems with harmonics with PWM creating a "pulsating" brightness effect with certain colors.

Now I'm hunting for a way to prevent this strobe effect.

Is there perhaps some way to randomize the pulse frequency with PWM so it creates the same aggregate on/off level every N cycles without using a specific frequency?

Are there any other ways I might be able to overcome this?

Thanks!