Drawn for my fanfiction, Choices: [link]

This is basically what I had in mind when I had Fixit describe the laser core. The laser core is a box. The spark casing is inside the laser core, secured with clamps connected to wires feeding to the rest of the body. The spark is inside the spark casing, and it is all pretty and glow-y. The sparkles make it look pretty. Here's what it's all made of:

Laser Core = metal
Spark Casing = Cybertronic glass
Spark = energy

My idea for the spark casing is that it is always the same color--a pale, aqua blue--but the casing is shaped differently depending on the mech's personality. It can be shaped like any one of the five platonic solids, depending on which of the "Big Five" personality traits dominates their existence.

Openness - Icosahedron
Conscientiousness - Cube
Extroversion - Octahedron
Agreeableness - Dodecahedron
Neuroticism - Tetrahedron

Not to say that someone with this or that shape is ONLY agreeable or neurotic or what-have-you. What shape the spark is only determines what personality trait instinctively gets precedent over others--it does not dictate the entirety of their personality nor how one necessarily chooses to act.

(For pictures of the platonic solids, see here: [link]
For more info on the Big Five traits: [link])

Now, who can guess what Starscream's spark is shaped like?

Disclaimer: Don't own Transformers. Go look to Hasbro or Takara for that.