Conditional formatting cell with "space" character

In a range, I try to make a conditional formatting like this :
cell with single space character → background red
cell with double space character → background green
cell with triple space character → background blue

but when I edit, the space become blank.
I try the ’ ’ and " ", but not work, libre replace the condition " " or ’ ’ to blank in condition field.

Is there some alternative to represent “space” character?

what is your OS and LO ver.
I test use " " in condition field and it work.
On win7, LO 4.0.5

Mine LO 4.0.5 on Ubuntu 13.04.
I end up by use character and sets the font color equal to background color. It not make any sense since in programming 32 is not equal null.