Violet
No, the visible frequencies of sunlight are not present at equal intensities. The intensity varies across the different colors in the visible spectrum, with some colors having higher intensity than others. This variation in intensity is what gives rise to the different colors we perceive in sunlight.
Technically it doesn't. The retina has several different types of cells with different sensitivities to different frequencies. Their various outputs are interpreted in the brain (occipital lobes) into color.
No frequencies in that range appear on the list you provided with the question.
Orange
Light is energy radiated in specific frequencies by a physical, chemical, or nuclear reaction. Visible light is absorbed or reflected by physical objects, enabling them to be viewed or detected. The term "light" is also applied to frequencies at either end of the normal visible spectrum, as the infrared and ultraviolet ranges.
Because it has no color, therefore nothing to absorb. With light energy, surface colors absorb and reflect various color frequencies (electro-magnetic wavelengths). For instance, blue paint reflects higher frequency wavelengths which our eyes see, and our brains interpret, as blue values, and it absorbs lower range frequencies we would interpret as red and yellow. White surfaces reflect high quantities of all of the visible range of frequencies of electro-magnetic wavelengths, so the frequencies reflected back at the viewer contain all visible color ranges that are contained in the light hitting that surface and appear the same color.
The colors that we call orange or red are particular frequencies of visible light. An object that reflects mostly the light in a particular frequency will "look" that color. It is the compounds in the skins of fruits that absorb and reflect light in different frequencies, In the case of the apple, the compounds inside the skin absorb a completely different range of frequencies, and are therefore a different color.* Objects that absorb almost all colors of light appear brown or black. Those that absorb little light of any frequency appear white.
Sunlight is actually light waves of different frequencies. Some of these waves are part of the visible light spectrum (ROYGBIV), and therefore sunlight appears white, a combination of all the frequencies in the visible light spectrum. Light waves with lower frequencies appear more red or orange. Light waves with higher frequencies appear violet or blue. When sunlight shines down through the atmosphere, the particles in the air scatter the light waves of higher frequencies, therefore spreading the waves in different directions in the sky (This is why the sky appears blue). The lower frequency waves reach our eyes mostly undisturbed. Since sunlight has light frequencies dominant in yellow, that's the color we see.
No, sunlight contains only three frequencies that appear together as white light
The cones in the retina of our eyes are sensitive to certain frequencies of light within the visible light spectrum (ROYGBIV). Light waves with longer wavelengths (within the visible range of frequencies) are perceived to be on the red, orange, yellow side of the spectrum, while higher frequencies/shorter wavelengths of light appear blue or violet.
Suddenly becomes visible. Appear.
No. they appear all the time. they are visible at night in the northern hemisphere when there are no clouds and are more visible the further north that you are.