Color change in indicators

Methyl orange indicator changes color to red and yellow with an acid and base respectively.
I am unable to understand why this color change takes place.


Searched on Google about the same with litmus paper and some answers said that litmus paper contains an acid an a base with color red and blue respectively. 
But what about phenolphthalein it does not show any color change with acid.




Phenolphtalein is formed of three phenyl rings which are attached to the same Carbon atom. In the basic form, this central Carbon atom is part of a double bond joining it to one of these phenyl rings, which has a quinonic structure. The delocalization of the pi electrons is possible over all rings simultaneously. The rings are coplanar, and define is a huge domain. This is a huge "box" for the electrons, and the electronic transitions are low energy, that is in the visible. 


In acidic solution, the central Carbon atom is related to four simple bonds. The phenyl rings are not coplanar. Their pi systems are not even delocalized over the whole molecule. The domain available to the pi electrons is limited to the phenyl rings, which are about three times smaller than in basic solutions. So the electronic transitions are high energy, in the UV region. And the phenolphtalein is colorless.


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