roi: tweak color scale

this should be more colorblind-friendly

ts/roi.ts

@@ -49,7 +49,7 @@ async function render() {
 function color(n: number, low: number, high: number): string {
 	// scale n from low..high to 0..1 clamped
 	const scale = Math.min(Math.max((n - low) / (high - low), 0), 1);
-	return `color-mix(in oklch, #0c8 ${scale * 100}%, #f70)`;
+	return `color-mix(in xyz, #0aa ${scale * 100}%, #f80)`;
 }
 
 setupPopover();