Why do my unread messages change colors?

[AC Question]

Hi, so I currently have the Galaxy S6 and I use the Samsung Messages app for texting. Whenever I get a new text, the icon will have a red bubble with the number of unread messages in the upper right corner. Every now and then the bubble is a yellow-orange color and I can't figure out why it would do that and I can't find a setting to keep it from changing. Does anyone know why that little bubble would change colors?