Analysis of 'In the Pink'

So Davies wrote: ' This leaves me in the pink. '
Then scrawled his name: ' Your loving sweetheart Willie '
With crosses for a hug. He'd had a drink
Of rum and tea; and, though the barn was chilly,
For once his blood ram warm; he had pay to spend,
Winter was passing; soon the year would mend.

He couldn't sleep that night. Stiff in the dark
He groaned and thought of Sundays at the farm,
When he'd go out as cheerful as a lark
In his best suit to wander arm-in-arm
With brown-eyed Gwen, and whisper in her ear
The simple, silly things she liked to hear.

And then he thought: to-morrow night we trudge
Up to the trenches, and my boots are rotten.
Five miles of stodgy clay and freezing sludge,
And everything but wretchedness forgotten.
To-night he's in the pink; but soon he'll die.
And still the war goes on; he don't know why.