Hi,
1. I suppose that you could do that with HikaShop by having all the color variants of the product with the same name. That way the breadcrumb would display without the color variation. And then, in the listing page, you would add a condition on the MySQL query to not retrieve more than one product with the same name (you could do that by developing a small hikashop plugin to modify the MySQL query). That way, when you filter on a color, you would get the product of that color, and otherwise, if no color filtering is done, you would get the first one "randomly" and the others would be ommited.
2. Well, that would require some development to first track what products are seen by who in the database so that it would then be possible to have some code to use that data to display a listing of products also seen by others synchronized with the current product.