The colour scheme looks good, but I agree about lining being dead boring.........
The color choice is pretty limited in the uni Paint markers, black, white, gold, silver, bright red, bright blue, bright green, bright orange, bright yellow and a fetching shade of pink. Tamiya also sell something similar, with much the same colour range.
The non-metallic colours are fairly transparent, so the orange might be worth trying, as it may look more like buff when used over a blue background. Silver would look OK on the window frames, as they are usually unpainted aluminium on modern rail vehicles.
Many years ago there were paint pens available for touching up cars, which came in a very wide colour range. I used them at the time to line and letter a large 7 1/4" loco. Not sure if they are still available though.
I generally use a bow pen and Humbrol enamel for this sort of thing, but bow pens are getting hard to find and the learning curve is very steep if you've never used one.
Regards,
Graeme