In preparation to use RGBW (as explained here http://www.partsnotincluded.com/neopixels/fastled-rgbw-neopixels-sk6812/ ) I changed my sketch

In preparation to use RGBW (as explained here http://www.partsnotincluded.com/neopixels/fastled-rgbw-neopixels-sk6812/) I changed my sketch from
CRGBArray<NUM_LEDS> leds;
to
CRGB leds[NUM_LEDS];

This forced me to also change
leds(0, NUM_LEDS - 1) = CRGB::Black;
to
leds[0, NUM_LEDS - 1] = CRGB::Black;

Now my sketch does not work as expected, but I get no errors while compiling.
Is leds[x,y] not supported?

Do I have to use a for-loop to address a range of leds?

Nevermind. I think this hack has to many limitations.
I would need to modify too much of my existing project.