Since you are using Mapsource, colour your track (in properties, I like green) before using 'send to device'.
You can also colour it in the Etrex, its just a bit easier to do it in Mapsource.
Also although uploaded tracks usually default to 'show on map', occasionally they don't, and I've never been able to work out why (ie what it is about the saved track that switches it off) so I always check each one in the Etrex to make sure the 'show on map' tickbox is enabled.
Etrexes can't utilise any Track or Route information that is placed on the memory card. Only maps, and custom POIs.