The first product I tried was the Oscar Blandi Luce Sheer Gloss treatment. The product, which is "a rinse-out gloss...exclusively designed to lock in pigment added to restore shine," did pretty much nada to add shine to my hair, even after I used it a few times.
The next product I tried was Redken's All Soft Gold Glimmer perfecting shine treatment. I reasoned that I would have better luck with this one as, duh, it is a leave-in treatment -- hence, meant to leave in shine. As applied to my hair when curly, Gold Glimmer simply weighed it down and made it greasy without adding any extra shine. As applied to straight hair, the result was somewhat better but I still didn't love the heavy, greasy feeling. I definitely would not apply the product close to my roots for fear of having to wash my hair all over again.
It is possible that my hair simply sucks up light like a black hole, but my next course of action is going to be a professional glossing treatment instead of trying other glossing products. My appointment is next Saturday - wish me luck!