WS2812B are only white on custom board
The WS2812B chips are very sensitive to timing. They rely on pulses being just the right length for things to work.
It is common if the timing is off that you just end up with white.
Since you have a blank chip that you have never put a bootloader on the fuses will be set wrongly for your configuration. By default a chip comes configured for the internal 8MHz oscillator. That means that everything will be running at half the speed.
You need to set the fuses to use the 16MHz crystal so that it matches the F_CPU setting of 16000000 in the board configuration. Either that or use a board configuration that expects to run at 8MHz.