Benzene itself is transparent in the visible because it absorbs in the UV. However substituted benzenes are often slightly yellow because the absorption band is shifted slightly into the blue (blue is absorbed, leaving red/yellow). Naphthalene will be even worse.
You need optical transparency over the entire visible range?
As I recall, my PhD lab collaborated with a group that made optical waveguides out of some of our compounds, dissolved at high concentrations in DMSO. But those were intended for the NIR, not visible. I'm not sure what people use for the visible region, but I'm sure it's been done.