Yoong Liat wrote:
But now I'm confused. Some members say it should be hyphenated.
Multi-word adjectives should be hyphenated. But most native English speakers don't know this and even those who do often neglect to do so. That's why you get conflicting opinions.
coluber2001 confused you because he attempted to illustrate that the words "darker coloured" don't necessarily construct a multi-word adjective. But to be honest I'm not sure that he succeeded since his examples change structure and can still be seen as using a multi-word adjective.
Here are different examples that might be clearer:
The darker, coloured image is my favorite. (This is two adjectives).
The darker-coloured image is my favorite. (This is one adjective).
It could be darker and colored or just comparatively darker-coloured.
One trick that may help you is to use "and" where you would put the hyphen and see if it makes sense. If not, then use the hyphen.
Your particular example is easy to confuse so I'll use an easier one: two-car garage.
It is a two-car garage. If you say "it is a two and car garage" it makes no sense. Compare it to multiple adjectives (as opposed to a multi-word adjective):
It is a big, blue garage. If you say "it is a big and blue garage" it is awkward but makes sense. So don't hyphenate the adjectives as they are separate.
P.S. I'm not sure if my comma between big and blue in my example is correct. It's a weird area of punctuation and I'm very, very bad with commas.