This looks very similar to the infamous "look and feel" lawsuits lauched by Apple, most infamously against Microsoft. Apple's claims, that the holistic visual impression of a product can be copyrighted independently of the copyrightability of any of the particular elements, has AFAIK never been tested in a lawsuit, so you are in a legal limbo, although the judgements that touch on it have generally been somewhat hostile to the idea. I further think that the general style of an artist is harder to argue that the kind of design issues Apple were (and still are) defending, which were part of complex UI interactions, and could be said to have semantic significance from that role.
So there is some risk, but I say it is a risk a small or freelance graphic designer/outfit can take, provided:
- You are extra- careful about not infringing concrete copyrights or trademarks;
- If you do work on behalf of a client, you fully inform them of what you understand of the legal risks;
- You are in Delaware, right? You might still be exposed to laws of countries with harsher copyright regimes, like the UK;
- You are responsive to concerns raised by whoever you pay tribute to; and
- You check any legal intuitions you have with people who have the kind of legal expertise that aren't shared for free on Stack Exchange sites.
Furthermore, our culture would be a poorer place without tributes, so taking small, well-judged risks of this kind is doing something worthwhile.