The tooltip background color cannot be changed

maifan the color you're referring to is defined in the UI theme (Editor.ToolTip.errorBackground color key). Unfortunately, at the moment it cannot be customized via any UI setting now. You can only develop a theme plugin to override this particular color or look for an existing third-party theme on the JetBrains Marketplace that would ensure a better experience.

There's a general feature request to allow customizing themes, feel free to upvote IJPL-55524 and follow it for updates (see this article if you are not familiar with YouTrack).