At the moment the sun flare of every system is taken randomly from the list of flare files in \textures\. That's why the look of the sun of a system changes with every game. To get a unique look for every star system it would be nice to add a flare-tag to the .system file just like for the system background garphics...
Maybe it could look like this:
<system name="Sol" background="backgrounds/blue_galaxy1" flare="flare1.png" ...>