Hi,
I would recommend to not use characteristics for your color selector. It will solve both your problems and allow to have products with images selectors and it will work fine with the options.
You want to create 5 custom fields of the table "item" and of the type "radio" via the menu Display>Custom fields. Then, for their values, you want to have translation keys like that:
IMAGE1
IMAGE2
etc
Then, in your HikaShop configuration, add translation keys like that under the languages tab:
IMAGE1="<img src='http://mywebsite.com/myimage.jpg'/>"
www.hikashop.com/download/languages.html#modify