The colors have a strong effect on the human body and mind. The Planetary vibrations continuously exercise an influence through our sensory nerves. Similarly, also at the time of birth of a person, he might suffer from a deficiency of certain rays or colors, which causes various imbalances in the body, leading to diseases and problems.
The Solar, Lunar, Planetary and Stellar bodies supply energies of different wavelengths, in varying intensities and frequencies etc. The gem-stones counter the harmful rays and capture the beneficial vibrations, which, of course depends upon the particular case and the requirements on the basis of the horoscope of the person vary. Each horoscope would indicate different composition of vibrations to be avoided or those which are lacking according to the planets' influences.
This also makes it imperative that these stones should be worn with correct attributes like the name of the mine, weight, density, specific gravity, refractive index, in combination with metals of correct composition, on the right day and time etc., as per the requirement.
For eg. the Blue Sapphire or Neelam, being a strong crystal has an immense potential of capturing positive vibrations as also of deflecting the negative energies and may lead to a change in the whole course of one's destiny, BUT only if worn with correct and precise attributes. Or else it can be very harmful.