Question: When the pH is neatral, what occurs?
About the article "Vegetable", section "Color pigments".

Candidate passages:
 Acidosis refers to a "process" that causes a low pH in blood and tissues.
Acidemia refers specifically to a low pH in the blood.
In most cases, acidosis occurs first for reasons explained below.
Free hydrogen ions then diffuse into the blood, lowering the pH.
Arterial blood gas analysis detects acidemia (pH lower than 7.35).
When acidemia is present, acidosis is presumed. 
The pH level of a wine is the measurement of the amount of free (H+) hydrogen ions.
It is related to the titratable acidity level of a wine but differs in significant ways.
Low pH numbers indicate a high concentration of acids in a solution.
While pure water is neutral with a pH of 7, wine tends to be more acidic with a pH between 3 and 4.
As the acid levels in ripening grapes fall, the concentration of acids are lessening which means the pH level is rising.
Yeasts, bacteria, phenolic compounds such as anthocyanins which influence color all have varying tolerance to wines with high pH levels.
In general, wines with high pH value tend to have duller colors and less developed flavors and be more prone to wine faults caused by spoilage organisms which makes monitoring the pH levels of grapes during ripening a priority for viticulturists and winemakers.
While the rudimentary method of testing pH is to expose the grape juice to a pH indicator such as the strips used for a standard litmus test, the results are usually not as detailed and accurate as what is needed to evaluate ripeness.
Therefore, most wineries will us a pH meter that can give readings to an accuracy of plus or minus 0.1.
As with sugars and acids, the ideal pH levels to determine ripeness will vary.
For white wines, winemakers often look for pH readings between 3.1 and 3.2, while would be a maximum of 3.4.
If the pH is too high, it may be a sign that the grapes are overripe (or that the soil has too much potassium which will also influence pH readings).
While there are risks to letting the pH go too high, winemakers can counter high pH by adding more tartaric or malic acid during the winemaking.
However many viticulturists and winemakers uses pH readings as a strong boundary line for when to start the harvest. 
Halochromism occurs when a substance changes color as the pH changes.
This is a property of pH indicators, whose molecular structure changes upon certain changes in the surrounding pH.
This change in structure affects a chromophore in the pH indicator molecule.
For example, phenolphthalein is a pH indicator whose structure changes as pH changes as shown in the following table:In a pH range of about 0-8, the molecule has three aromatic rings all bonded to a tetrahedral sp3 hybridized carbon atom in the middle which does not make the π-bonding in the aromatic rings conjugate.
Because of their limited extent, the aromatic rings only absorb light in the ultraviolet region, and so the compound appears colorless in the 0-8 pH range.
However as the pH increases beyond 8.2, that central carbon becomes part of a double bond becoming sp2 hybridized and leaving a p orbital to overlap with the π-bonding in the rings.
This makes the three rings conjugate together to form an extended chromophore absorbing longer wavelength visible light to show a fuchsia color.
At pH ranges outside 0-12, other molecular structure changes result in other color changes; see Phenolphthalein for details. 
Corrosion or solution/chemical weathering occurs when the sea's pH (anything below pH 7.0) corrodes rocks on a cliff face.
Limestone cliff faces, which have a moderately high pH, are particularly affected in this way.
Wave action also increases the rate of reaction by removing the reacted material. 
Acid–base imbalance occurs when a significant insult causes the blood pH to shift out of the normal range (7.35 to 7.45).
In the fetus, the normal range differs based on which umbilical vessel is sampled (umbilical vein pH is normally 7.25 to 7.45; umbilical artery pH is normally 7.18 to 7.38).
An excess of acid in the blood is called acidemia and an excess of base is called alkalemia.
The process that causes the imbalance is classified based on the etiology of the disturbance (respiratory or metabolic) and the direction of change in pH (acidosis or alkalosis).
There are four basic processes: metabolic acidosis, respiratory acidosis, metabolic alkalosis, and respiratory alkalosis.
One or a combination may occur at any given time.