Yellow USB-A ports usually mean Always On charging, but the particulars are up to the manufacturer.
A yellow USB port usually marks an "Always On" port, meaning it will continue to charge your device once you turn the computer off. It's one of several colors on USB-A ports, but none are an industry standard.
For example, the USB Implementers Forum (USB-IF) recommends one insert color, a specific blue, to help people tell the difference between USB 2.0 and USB 3.0 ports. However, this is just a suggestion, not a mandate. Every other color, yellow included, is a convention manufacturers can follow or not.
Lenovo, for example, jumps around with colors. The older IdeaPad Y400 and Y500 feature yellow USB-A ports that are specifically for Always On charging. Later Lenovo models dropped the yellow entirely and replaced it with battery icons.
Yellow USB-A ports are not a common sight because they're a specialty feature that manufacturers only include on specific enterprise or business laptops. Manufacturers are also shifting toward symbols instead of a variety of colors.
A battery symbol next to a USB port indicates a port that's good for charging. A trident symbol also indicates the USB implementation, like USB 3.0 or USB4.
