And "yellow" is a bit of a subjective term. In Photoshop pure Yellow is a mix of colors: pixels 255 Red and 255 Green. Do you want to include 254 Red and 253 Green? Or 253 Red 249 Green and 10 Blue?
It is difficult for quantification purposes to pull out "only Yellow". You can use Color Range selection, but that is not exact enough IMO for data analysis, unless you have very controlled parameters.
Scripting may help with selecting/identifying pixels containing both Red and Green but no Blue data. But that is way above my pay-grade.
Can you give more detail for your request? Is it to quantify areas of double-labeling in cell photo-microscopy?