If your question is really about making yellow on a screen or with lighting, you’re in additive colour mixing. That means yellow comes from mixing red and green light at the right intensities—often called RGB mixing. Blue doesn’t play the same role here as it does in paint, because you’re building the colour by adding light, not subtracting it.
On computers and phones, “yellow” is typically represented by colour values in software—such as a high red plus a high green and a lower blue. If you want to match a printed or painted yellow, your monitor won’t always match it exactly because of differences in colour space and how devices render colour.
Matching yellow across devices
If you’re designing content that must look consistent, calibrate your display if you can. Even without calibration, keep the brightness consistent while you adjust. A yellow that looks perfect at one brightness can shift when viewed on a different screen.
For projectors, room light matters. Yellow on a projector is much more sensitive to ambient light than you might expect. Darken the room, test with your specific content, and don’t rely on what the colour looks like in a bright showroom environment.
