Guys,
FCOM 22 20 40 30 "Predictions Displayed on the ND" tells us that the 'D' indicates:
- The point at which the ac is predicted to decelerate for the approach (and thus switch to the approach phase)
- Magenta, if in managed speed and NAV or approach mode is engaged
- White if in selected speed or HDG/TRK mode
- Automatic deceleration only occurs when displayed in magenta
mcdhu