Whites work just fine. You can get any color white you want in an LED, and there are many that are rated in kelvin. If you carefully read the specifications for a white made by a reputable manufacturer you will see that like other forms of lighting, LEDs have a dominant color, or color temperature, and a spectrum of others. This spectrum is the only reason to frown on whites for plant lighting. It is wasted energy, like the energy that is wasted in an HID light. That doesn't mean the plants won't grow, it just means that the most desired color is not the dominant one. Most people believe that colored LEDs don't have a spectrum, but that's far from true. It's just that the spectrum in single color LEDs is not as varied as it is in whites. For example a 660 nm LED has a spectrum from about 620 to 700, and it is wasting energy in the same sense that whites do.

One thing that we can do with LED whites that we can't with other forms of white light is change the color. Again look at the specs, and notice that the LED is rated to be any color from, for example 3000K to 10,000K. Again this is only the dominant color, and it all depends on what kind of current you supply, plus a few other less significant factors.