Usage of "one" and "ones"

[Banglardon]

I have a problem understanding the usage of one and ones and when they can be omitted. Here are some examples:

1- There are many colour of roses but I like blue and red.
2- There are many colour of roses but I like blue ones and red ones.

Here is an example from this site. http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv175.shtml

A- What / Which colour trousers would you like? Brown, green, blue, orange or maroon?

Could you please tell me why ones has not been used there like brown, green, blue, orange or maroon ones?

Then can I say:

B- Which colour bag would you like? Red, blue or green?

Or should I say?

C- Which colour bag would you like? A Red one, a blue one or a green one.

 

[emsr2d2]

I have a problem understanding the usage of one and ones and when they can be omitted. Here are some examples:

1- There are many colours of roses but I like blue and red.
2- There are many colours of roses but I like blue ones and red ones.
3 - There are many colours of roses but I like blue and red ones.

Here is an example from this site. http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv175.shtml

A- What/Which colour trousers would you like? Brown, green, blue, orange or maroon?

Could you please tell me why "ones" has not been used there, [STRIKE]like[/STRIKE] as in "brown, green, blue, orange or maroon ones"?

[STRIKE]Then can[/STRIKE] Which of the following should I say?

B- Which colour bag would you like? Red, blue or green?
[STRIKE]Or should I say?[/STRIKE]
C- Which colour bag would you like? A red one, a blue one or a green one.

See above. I have added a sentence (numbered 3), which is more natural than your two (corrected) suggestions. You don't need to add anything after the colours because it's already abundantly clear that you are talking about a pair of trousers. Also note that starting with "There are" is unlikely to be how a native speaker would say it. I'd say something like "Roses come in many different colours. My favourites are red and blue ones/roses."

Both B and C are possible. Again, there is no need for "one". B uses fewer words to express the same thing.