I'm doing research on how the pigmentation of fish. I want to know how could you change it with the help of genetic modification. I have some Silver Dollar fish (Metynnis argenteus) and I want to make them have a shimmering gold appearance like a gold piranha. I was told by someone on reddit that it would be much easier to breed them to create the desired phenotype, but I don't think that's possible since they don't produce many observable differences in pigmentation. So, I want to know if anyone has any experience with this and could help me out. I'm still trying to understand all of this so it would help to not be too technical.
I think you need to clarify what kind of research you are doing. Breeding and genetic modification might both produce the desired result, but in research it is likely not the main point (but instead getting to this result in a certain way and obtaining the insights from doing this).
There are many studies on coloring of zebrafish and guppies, producing all kinds of differently colored mutants... but I doubt that one can predict the result in advance, since the link between the genotype and the phenotype is not well understood yet. In fact, understanding this link is precisely the point of these studies. You can start with exploring the work done in this domain by Nüsseln-Volhardt's group, see, e.g., here.