Control the individual brightness of LEDs on WS2812B
With WS2812B LEDs you supply the binary values for Red, Green and Blue of each LED. Each time a new serial bit stream is sent to the LED string all of these values need to be provided. I really suggest that you read the data sheet for the LED and you would already know this.

It is possible to scale the RGB value for each LED by multiplying each of the three LED binary values for the Red, Green and Blue by the factor. To brighten use a factor > 1.0 and to dim use a factor &lt; 1.0. You must use care to make sure that the resulting calculations stay within the size/range of the normal binary values for each color. For example you cannot program a color value > 255 or less than 0.