Titanium dioxide is the best adhesive in enamels, the products treated by TiO2 will get more lubricous, and have better acid resistance, of course, have better appearance, and luster.
Early humans would have considered colors as simply hues of black, white, or red, which sounds kind of crazy, but there's actually modern day evidence for this.
While violets are spectral colors, meaning there is a single wavelength of light for various hues of “violet”, “purple” is actually a combination of blue and red.
Even if you look at a color picker in Photoshop, it's clear that a dark or navy blue isn't actually that far from being black, and is quite far from other hues which we would still call blue.