I know it is not etiquette approved, asking to contribute towards a honeymoon, but I really don't understand the big deal. I know I will be getting the couple a gift of any wedding I attend. I know what I can and will spend. So, what difference does it make if I buy the happy couple a set of china or contribute to a fund for a honeymoon? I am still spending the same amount of money that I would spend. And why give them some china that they might never use, but help towards the gift of a lifetime that they just might remember fondly forever and tell their grandchildren about the fabulous time on their honeymoon?
Just my humble opinion.
You mentioned green eyes, is this jealousy because they are choosing a honeymoon that you would love to do but are not doing for whatever reason?
If you do not want to contribute, then don't. Buy them what you think they might like for their new home or whatever you desire. No one says you have to contribute towards the honeymoon fund. And if asked, you don't have to say your feelings, just say, "Oh, I saw this and thought of you guys and I bought this instead!".