In this Makefile, you can find all the triggers chosen for a 5.4 kernel.
But I noticed that by cat /sys/devices/platform/leds/leds/led0/trigger, some triggers are not listed (e.g. "pattern" and "activity").
It turned out that they are compiled as kernel modules but not loaded by default.
They are located under /lib/modules/[your kernel ...
Sounds like it -might- be working the way you need it to. What you're missing is a diffuser/combiner for the light coming from the LED. When you look directly at an RGB source that's not diffused you'll see the individual colors. As for dark grey vs white, that's a matter of relative intensity (assuming everything's balanced).
I've used ping-pong balls for ...
RPi.GPIO dutycycles are in the range 0 to 100 and represent a percentage of total power. So a dutycycle of 0 is off, 100 is fully on, and 50 is half power.
There is quite a lot of changes I would make to the code. Basically I would have an initialisation section where all the stuff which should only be done once would be placed.
Presumably rather than GPIO to LED+ then LED- to ground your connection is 3V3 to LED+ then LED- to GPIO. That would account for the dimming rather than brightening.
I have ignored the resistor which will be somewhere in series in both the above cases.
You can either change the LED connections or reverse the while loop to count down rather than up.