The phone's charging color is yellow because Low Battery Mode is turned on, which is a mode of increasing battery life of the iPhone, and the iPhone will temporarily reduce background activities such as downloads and email acquisition until the iPhone is fully charged.
If you want to turn off the low battery mode, you can go to the [Settings] - [Battery] option and turn off the Low battery mode, so that the battery icon will return to green, or very low battery red;
Generally, it is green when fully charged, and it will show yellow when the battery is used to half or less, and it is generally red when the mobile phone is used to less than 20%, so the battery power is different, and it will show different colors.
The charger shows yellow, which means fast filling.