PowerPoint blends a gradient of exactly two stops at 0% and 100% in linear
light, with the second colour's share following an S-shaped curve (black to
white is 105/186/238 at a quarter/half/three quarters, not 64/128/191).
Gradients with more stops, or a stop moved off an end, stay linear in sRGB.
Measured with PowerPoint's slide export on shapes and backgrounds, in both
directions. The two-colour case is expanded into sixteen pieces per
segment so vello's sRGB interpolation draws the same ramp.
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
