As an example, imagine a game where each person can have 0+ marbles, each of which are entities. How could I create a list with each person, along with any blue (not any other colors, possibly creating multiple rows per person if they have more than one) marbles they have, still displaying them even if they don't have any. I'm thinking I would use an optional relationship, but if I put a filter, it completely hides the row if it has a match that doesn't meet the filter instead of treating it as if the relationship had no match at all.
Note: In the actual site, the "People" are ECK entities, and the "Marbles" are nodes with entity references to the "People".
EDIT: This is not a dup of Views and joining content types on specific field in Drupal 7 as that discusses how to create an required relationship in Views, whereas this one is about filters on optional relationships.