Paint timeline slots spent in a cable measure blue

ui.go

@@ -40,6 +40,7 @@ var (
 	uiCrit     = rgb{0xd0, 0x3b, 0x3b}
 	uiCellOK   = rgb{0x0a, 0x5d, 0x0a}
 	uiCellNA   = rgb{0x3a, 0x3a, 0x37}
+	uiCellMeas = rgb{0x20, 0x4d, 0x83}
 	uiAccent   = rgb{0x39, 0x87, 0xe5}
 )
 
@@ -432,12 +433,16 @@ func (d *display) drawColHeaders() {
 	d.hairline(d.rowYs[0] - 1)
 }
 
-// One row of history cells: na for a slot with nothing believable (never
-// sampled, or spent inside a measure), otherwise judged by the row.
+// One row of history cells: na for a slot never sampled, the non-committal
+// measure color for one spent inside a cable measure, otherwise judged by the
+// row.
 func (d *display) heatRow(rowY int, hv histView, judge func(histSlot) rgb) {
 	for k, s := range hv.slots {
 		c := uiCellNA
-		if s.sampled && !s.measuring {
+		switch {
+		case s.measuring:
+			c = uiCellMeas
+		case s.sampled:
 			c = judge(s)
 		}
 		d.heatCell(rowY, k, c)