In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
It is permissible for woman to wear jewellery which is plated with rose gold. In principle, women are only permitted to wear rings made of gold or silver. It is not permissible to wear rings made of any other metal. 
Since imitation rings are not made from real gold or silver, it is not permissible for women or men to wear them. Similarly, it is not permissible to wear rings made of platinum. However, it is permissible to wear a ring which is not made of silver, but is plated with silver.
White gold is similar to yellow gold, except that platinum, nickel or zinc has been added to it instead of silver or copper. It is well known that adding silver or copper to gold does not alter the fact that it is gold, which also applies to adding palladium to it.
Therefore, as a principle, if the ring is made of an alloy of different metals then the ring will take the ruling of whichever metal is predominant in the alloy. For example, if the finger ring is made of an alloy containing 37.5% platinum, 10% silver and 52.5% gold, the ring will be considered to be of gold and therefore it will be permissible for a woman to wear it. (As for other types of jewellery of women — such as necklaces, ear rings etc. — they can be of any material.)
Women can only wear gold and silver rings, or rings which are plated with gold and silver. Therefore, it will not be permissible for a woman to wear a ring which is plated or finished with platinum or rhodium because it does not display gold or silver.