Psychology
A token is a decision about how a reader should feel before they have read a word. These are the effects each choice is buying, so that changing one is a deliberate act rather than a preference.
Cool neutrals read as instrument
The surface ramp is a blue-cast grey rather than a warm paper. Warm greys read as editorial and human — good for a magazine, quietly wrong for work that wants to be judged as rigorous. A cool ground puts the reader in the frame of mind of looking at an instrument, which is the right frame for a case study about decisions.
Near-black, never black
Ink is #0A0C10, not #000. Pure black against a light surface produces a hard optical edge that reads as cheap, and it is the single most common giveaway of an interface that was never looked at closely. Pulling a few points of lightness and a trace of blue into the ink makes long passages sit on the page instead of vibrating against it.
Tight radii read as precise
The corner radius is 2–4px, and almost never more. Radius is the fastest signal of register an interface has: large radii read as friendly, consumer, soft; small radii read as exact, technical, considered. This is the one token to change if the whole system ever feels like the wrong kind of product.
Scarcity is what makes an accent mean something
There is one accent hue. Its job is to mark the single most important thing in view, and it can only do that while it stays rare. A second accent does not add a second meaning — it removes the first one. If two things on a page are blue, neither is important.
Speed reads as competence
Almost every transition runs at 140–160ms. Below roughly 100ms a change is perceived as instantaneous and the reader cannot follow what moved; above roughly 300ms they start waiting on the interface. Sitting just above the lower bound gives the reader the thread of what changed while never making them wait for it.
Small type next to large type reads as confidence
Interface text sits around 15px while display text runs to 58px. A wide gap between the two is what makes a layout feel composed rather than uniform. A system where everything is 16–24px has no voice, because nothing in it is allowed to be either quiet or loud.