What does idiom mean: paint the town red?

[Henna]

English Language Tests, Intermediate level

ESL/EFL Test #702 "English Slang Idioms (444)", question 5

"We haven't gone out as a group for a while. Why don't we all get together and paint the town ......... tonight?" Lilly said to the girls.

(a) new
(b) right
(c) red
(d) over

English Language Tests, Intermediate level

ESL/EFL Test #702 "English Slang Idioms (444)", answer 5

"We haven't gone out as a group for a while. Why don't we all get together and paint the town red tonight?" Lilly said to the girls.

Correct answer: (c) red

Your answer was: incorrect
"We haven't gone out as a group for a while. Why don't we all get together and paint the town new tonight?" Lilly said to the girls.
_________________________

Why did you use "red" and not "new" or anther word?

[Lost_Soul]

Because of this: http://www.phrases.org.uk/meanings/paint-the-town-red.html
(a fixed expression)