Definition of «than red ones»

The phrase "than red ones" is a comparison between two things. In this case, it means that the speaker prefers blue flowers to red ones.

Or keep it savory with green apples, which contain less sugar than red ones. (dailyburn.com)
I agree, this skirt is super versatile (more than the red one I think). (have-clothes-will-travel.com)
Your baby's blood contains much fewer white blood cells than red ones, although your baby's body can already increase production of white blood cells to defend itself against infection. (pregnancy-baby.com)
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