According to Red Sea and others, the eight light metals, including iron, manganese, cobalt, copper, aluminum, zinc, chrome and nickel. These are for green/yellow, but I'm not sure what's specifically for yellow.
The thing with yellow is there are almost no truly yellow corals. I am not saying there are not yellow acroporas rather that usually what we see as yellow is a blend of multiple non yellow color pigments. With the right ratio of Blue to Red to Green our eyes can see the coral as yellow. The thing is there are so many factors that effect all of these pigments that it can be nearly impossible to maintain yellow. Shifts in lighting or trace elements can make yellow corals turn orange or green very quickly.
While I have not seen a pigment analysis of every coral I have never seen an analysis of acropora that shows any true yellow pigment. I do know that Porites, Fiji Yellow leathers, Turbinaria, have true yellow pigments but that is about it.
Unfortunately there is no great way to maintain yellow acropora long term. If you want something yellow I would look at the few species of coral that have true yellow pigments.