// modified from https://imagej.nih.gov/ij/docs/examples/stained-sections/index.html, accessed July 2022
run("RGB Color");
run("RGB Stack");
setSlice(2);
setAutoThreshold("Default"); 
getThreshold(min, max);
waitForUser("set the threshold and press OK, or cancel to exit macro") 
run("Set Measurements...", "area area_fraction limit display redirect=None decimal=3");
run("Measure");
selectWindow("Results");