jedi_mike,
I have not tried using pencil color to paint straps. I use a very fine brush (or chinese brush) to paint such small/narrow details.
For ready-built trees: Try 2nd Floor Bldg B Megamall infront of the escalators near the restrooms. They sell railroad kits and also trees. However, these are very expensive about P200 per tree (4 US Dollars).
Suggestion: There is a hobby store in Makati Cinema Square (forgot the name) that sells foliage and static grass. I big bottle costs about P450 (9 US Dollars). This is enough to make you lots of trees but of course you have to do the trunk and branches by yourself. Check also some arts supply stores in Quiapo you can find some really interesting items there used for architectural scale model buildings.