The answer is
All in all: out of bed! Time the morning to greet!
Definition of ROUST.
Minus one and the statesman is losing his seat.
The statesman is OUSTed.
Minus two: it's a hue or a kind of a smirch.
RUST can be a colour or a smirch.
Minus three, in a way, nothing short of a perch.
ROST - one letter short of a roost.
Minus four, time to flee! Run away in defeat!
The fleeing army is in a ROUT.
Minus five, a big rat a king's daughter might meet.
Excellent riddle. Once I got the right answer, pretty much everything fell into place perfectly; nothing else could have fit the clues.
I got the last line first (being a fantasy buff probably helped - I'd had that particular work in mind for a long time even when I was thinking the answer would be PEA), and then the second-to-last line followed quite easily as the two words are similar.
At that point I was confused, having assumed each line described a word with one fewer letter than the previous line. But the singular version fit better than the plural for the second-to-last line, and I had a niggling feeling that maybe the numbers referred to positions rather than numbers of letters. And when I tried this idea, it worked perfectly right away.