To be super-pedantic, the correct character is a non-breakable half-space (unicode 0x202F). It actually makes sense: it shouldn't be breakable, or the text layo

To be super-pedantic, the correct character is a non-breakable half-space (unicode 0x202F). It actually makes sense: it shouldn't be breakable, or the text layout would be ugly (the colon starting on a new line?). And it should be reduced in size, because indeed you don't want a full space before a colon...