Despite the 'common knowledge', plants do utilize most of the visible light spectrum, even green, just in different amounts. And on top of that these white LEDs aren't just a single static white, their light spectrum are tuned to specific growth spectrum and can be ordered however you want, but all come out visibly to us as white of slightly different shades.

Those blurple lights are just awful, and not only do the LEDs have far less energy efficiency being old tech, but their supposed "optimal" wavelengths are anything but. They are blasting out extremely narrow wavelengths of light and trying to make it more continuous by using a bunch of slightly different narrow range colors, but it doesn't work as well as one would hope, especially when they are coming from different point sources.