What meaning red-green arrow in Class/Method in hint/search window?

Intellij IDEA has a feature called Machine-learning-assisted code completion, which is intended to prioritize code completion suggestion based on the choices made by other local users in similar situation. Basically, if the IDE thinks a suggestion is getting more relevant for your situation, it will be moved higher up on the suggestion list and a green arrow will be shown. If the opposite happens, then red arrow.