Here is how the weapon’s operation is described in the Alan Dean Foster’s novelization of The Force Awakens as presented in this article exploring how Starkiller Base’s weapon theoretically works; bold emphasis is mine:
At incredible velocity and accelerating exponentially, the
concentrated volume of quintessence escaped, transforming as it did
so into a state known as phantom energy and following the artificial
line of egress that had been provided. Assuming that the rotation and
inclination of the planet had been taken into account, the released
blast of concentrated phantom energy would travel along a perfectly
linear path, punching a small Big Rip through hyperspace itself until
it left the galaxy.
Unsure about how “phantom energy” works in the world of Star Wars, but what’s interesting about that description is how much it attempts to meld real world “dark energy” theory into the arbitrary logic of the Star Wars universe. Knowing that, then the big, bad, seemingly red beam of energy that Starkiller Base emits is basically created out of pure, concentrated dark energy. So since dark energy—according to Wikipedia—is defined as:
…an unknown form of energy which is hypothesized to permeate all of
Then what we might assume is the red “glow” we are seeing is perhaps not the actual core of the energy weapon’s punch, but possibly a side-effect glow created by the concentrated, dark energy of the weapon interacting with shields and atmosphere during it’s emission. And maybe that glow was nowhere near as dangerous for a viewer to witness at a reasonably safe distance—with some kind of shield in operation—than it seems on screen.