Lowering the kelvin reduces the percentage of blues. Is that correlating to color or spectrum
If it reduces the percentage of blue light put out by the fixture, then the color and PAR output of the light would be impacted.
The color temperature (measured in Kelvin) tells us how warm (red)/cool (blue) a "white" light looks to our eyes.
The spectrum (i.e. the wavelength of light produced) is the actual color of the light(s) produced by the light fixture (for example, a 395nm light emitting diode by itself produces a violet light) - how it looks to our eyes changes depending on all the colors that are produced at one time. For example, if you take a blue light diode (that only produces blue light by itself) and add some yellow, red, and green diodes to it all in one fixture, the light produced by the fixture would appear some variation of white to us (what variation would depend on how much of each light color is in the blend). The more blue added/other colors subtracted, the cooler the light; the more other colors (red, yellow, green, etc.) added/blue subtracted, the warmer the light.
So, the wavelengths and the actual amounts of light put out (measured for coral-keeping purposes as PAR - Photosynthetically Active Radiation) by each light-producing piece of a light fixture (in LED's the light producing pieces are the Light Emitting Diodes themselves) impacts the color temperature of the light as a whole.
All that to say that by decreasing the percentage of blue light the light fixture is putting out, you would change the color temperature (by removing blue light to make the color warmer), and you would reduce the amount of light (PAR) put out by the fixture as well.
Not sure what you mean by "the required blues"?
I think they're talking about the amount and wavelength of blue light needed to help the corals thrive photosynthetically. Long story short, coral zooxanthellae (and other kinds of algae) use certain kinds of light to produce energy for themselves and their host coral; certain wavelengths of blue light hit a photosynthesis "peak" that helps the zooxanthellae produce the highest amount of energy possible. Without enough blue light from around that peak wavelength, it could be tough for a coral's zooxanthellae to produce enough energy to help the coral thrive.
Also, for the OP, "white" light (6500K and others) can definitely grow corals if they produce the right wavelengths of light in the right quantities.
Blue light has been shown with deeper water corals to help them calcify (i.e. grow) faster in aquariums, but shallower water corals (like many of the ones we keep) can grow faster under white (i.e. full-spectrum) light. Which kind of light is better for a specific coral depends on a number of different factors (wild or captive, the type and amount of light it's used to, how long it has to adjust to different lighting, etc.), but both blue light and white light work fine.
White (full-spectrum) light (with some red light mixed in) is better for photosynthesis, as various photosynthetic pigments have "peaks" in various different light wavelengths (blue, green, red, etc.). The main peaks for both coral zooxanthellae, other types of algae, and plants are typically in the blue and red light wavelengths. Despite zooxanthellae having a peak in the red light wavelengths, however, corals don't like getting too much red light (in at least some cases, they actually actively avoid red light as larvae when they go to settle, and too much red light can kill otherwise healthy corals in aquariums over a long enough time).
These two paragraphs above get at two of the three main reasons why people run just blue lights: 1 - they believe it will help their coral grow faster (it might, dependent on the circumstances of the individual coral), 2 - (like Troylee mentioned above) they believe it will prevent algae growth/give coral an edge over algae in the tank (this is dubious, but it's possible there might be a very small impact of this nature), and 3 - they want their corals to fluoresce more (this one is definitely accurate; fluorescent colors will "pop" more to our eyes under heavy blue/violet light - think glowsticks under blacklight for comparison).
So, if you don't like the look of the heavy blue light, by all means, run white light - your tank will be just fine. Just be aware that changes to your lighting can impact your coral (and fish) color, health, and growth: if the corals are adapted long-term to heavy blue lighting (which may be the case if they've been in a blue-light tank for a while or if they're from deep waters), they will eventually adapt to the new lighting, but you
might see some slowed growth, dulled color, and less polyp extension during the adjustment period. If you want to ease them into the transition, then running just blue light for an hour or so in the morning and/or evening as suggested above may help, but I honestly doubt it would be necessary.
(If this block of text didn't scare you off and you want to read more on light and algae/coral, I have links available).
