Maybe you could do some simple things that would sort of set the scene for sex more along the lines of whatever dark fantasy you might be having? For instance, you could dress the part or adjust the lighting or put on appropriate music. I mean your H might be overwhelmed if you told him "I want you to be a sinister stanger in bed tonight." but he might seem like enough of a sinister stranger to make you hot if he would just agree to wear a black mask. You don't have to make a big deal out of it. If he seems reluctant or insulted by such a suggestion you could just tell him that it is the equivalent of getting a craving for spicy Indian food every once in a while even though you are generally happy with the excellent comfort food he offers up on a regular basis.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver
