For most of its life the body atlas used a green → amber → red ramp: the worse the entry, the hotter the spot. It is the obvious choice and it has one problem. Once several trackers share a body, colour has to say two things at once: which tracker is this, and how bad was it. A red knee could be a severe knee-pain entry or a mild entry from a tracker whose colour happened to be red. Colour cannot carry two meanings on the same surface.
The decision
Hue identifies the tracker; strength carries the severity. Every spot is painted in the colour of the tracker that owns it, and its opacity runs from faint for mild to near-solid for severe. The chips, the scrubber segments and both legends derive their opacity from the same curve the shader uses, so chrome and body can never drift apart.
The range widened at the same time. When colour separated mild from severe, the strength range could be narrow. Now that strength does the whole job, mild has to read visibly fainter than severe, so the floor dropped from 0.62 to 0.45 and the ceiling sits at 0.95. A spot with no reading at all sits at a fixed, calm 0.50: identity, not state.
What it buys
A body with three trackers on it is now legible at a glance. Psoriasis on the forearms, joint stiffness in the hips and knee pain in the knees each keep their own colour, and the hips being faint while the knees are strong says what it should. The history view, which washes each area by how often it was bad, uses the same language: strength is frequency there, hue is still ownership.
What it gives up
The traffic light’s one real virtue was that it needed no legend. Intensity needs a short one, mild to severe, which now sits beside the body. We think that is the right trade. A tracker whose colours mean something consistent across Home, the atlas, the charts and the report is worth a two-word legend.