Well, for me its totally a myth. We already have that rhinoviruses in our body system but the only thing that triggers that cold condition is when our immune system falls down due to a certain change, drop or rise of temperature in our body associated with the temperature of the environment. Because of this, sometimes our immune system can't cope up on those situations and will lead us to sickness.

Based on what i had experience, I usually get colds when there is transition of weather in our place (from summer to rainy seasons and vice versa). Yes, you can get colds too when there is a winter to summer transition of weather.

To put everything into one, its basically because of our immune system. There will be times that it is very weak. And to make our immune system so strong, there are only two ways I consider the most effective one:
HAVE ENOUGH SLEEP AND TAKE A BATH EVERYDAY!
:)