Meaning ofchanging color in disply window

Hi friends,

I have a quick silly question:

In display window ( when a code is running e.g. uniaxial text ) if the setting was on network mode ( showing interconnections of spheres). What Changing the colors from blue to red is representing, ?e.g. strain, stress,...
 I know it is a basic and fundamental question. However always there is a reason behind asking any questions even the silly ones! ;)

Thanks,
Seti