Some clarification on "coast mode" and ATC radar in general.
Different jurisdictions use different symbology - so it would pay to see if you can get a visit to a nearby ATC radar facility for some guidance. Post-9/11, not as easy as it once was, but worth exploring.
The picture linked to below is from the Athens, Greece, Area Control center. They use EUROCAT symbology, and since colors are used to define which controller has responsibility for which aircraft, "coast mode" is indicated not by color, but by replacing the "A" symbol for an aircraft with a "*".
In this image, there are two aircraft (top left, green) whose signals has been lost (likely due to high terrain blocking transponder returns, rather than a failure or crash, in this case) and are indicated by the * and a missing data block - i.e. in coast. The dots show their previous radar returns (one dot per sweep of the radar) - the straight lines show their projected paths.
(Personally, if this were MY screen, I'd be a bit twitchy. I've got two aircraft in coast mode, with no data on altitude, and with intersecting projected paths. One is farther away from the crossing point, but also moving much faster (spacing between prevous returns). But that's a different script....
)
http://www.hvacc.org/site/images/con...dep_vector.jpg