Why the ki users have 2 colors for the energy, one blue and one orange/red?
What you’re actually seeing isn’t Ki, but the burning oxygen gas reaction that occurs as a result of the “Heat” Ki emits.
You’ve seen a Bunsen Burner before, right? The more oxygen fuel a flame is given, the bluer and more concentrated the flame becomes.
https://en.m.wikipedia.org/wiki/Flame
Normally, Ki itself is invisible to the naked eye, like many natural gases, of course trained Martial Artists like Jam and Chipp can sense its flow.
Ki or “Life breath” as it is sometimes known, is the internal energy potential Humans have inside them.
You’ve heard of the phrase “Burning Calories”?
Calories are a measure of energy storage potential that allows us to function. Too much caloric intake and we gain bodyfat, not enough and we’re malnourished.
When Humans begin to harness and control that energy potential, it can transform in to a more potent force. That force is classified as “Magic” in Guilty Gear standards. Mana, in other words.
There’s different types of Mana, internal and external. External is typically residual emissions, but more commonly comes from the Backyard. Gears and Valentines tap in to Backyard Mana to supplant their immense power, especially with Gear Cells which are affixed gateways linking to the Backyard like a conduit.
Internal is what we call ‘natural energy’, it’s the energy we process and store in our Bodies after eating food.
The internal processing structure is defined as “Strings” to a Tuner like Kum Haehyun, only their trained eyes can see and manipulate it. They can tweak it to bring out our best energy potential, but we also tweak it every time we train our bodies or exercise.
At first, Ki is unseen and invisible, but with training, the body can emit it like a gentle wind.
As practitioners learn to control the speed and intensity of this 'wind’, it can produce varied results depending on the use of techniques and mastery.
Ki is the Foundation Magic, so it has different “routes” depending on the type of training. Jam’s Ki is based in the Fire element and becomes red to blue to white hot the more she refines it.
There are other practitioners who can manipulate Ki that results in Lightning, Water, or even Wind-based Magic!
Kliff Undersn takes it even further with his Reflex Roar, which is a highly concentrated blast of Non-elemental Ki, which is golden in appearance! He even shaped the Ki as a Dragon’s Fangs!
An example of Mana affecting the atmosphere is in the Babylon Information Flare event caused by the Cradle. The Japan stage where Ramlethal awaits is a sky swirling with a massive colorful “cloud” of Ki energy! Sin Kiske even remarks that the very sky looked like it was “bending” during that event! An unforgettable sight!