I tend to take the view that I should build the colours in the order of the prototype.
That is; paint the ties first, add the ballast (I use Woodlands Scenics medium grey blend), and then brush paint the rails with raw umber acrylic.
As I go, I wipe the rail heads with my finger. The paint washes off my finger in warm soapy water.
A bit of rust on the ballast looks realistic. Dots of black on the spikes.
Then I add some grass around the ties by putting on small dots of PVA and pressing static grass into the dots.
The residue is carefully sucked away with a vacuum cleaner - which helps to stand the the grass up.
Then dry brush the ballast with black in the middle.
Finally I brush on some weathering powders which tend to dull down the look of the grass.
I work the weathering powders right out to the sides, using different colours in each section of tracks.
Weathering powders help the look of the level crossing boards, as well.
Just sayin'