The tab content indicator is a feature that fades the icons of tabs with no content. When enabled it will send extra requests to the server, and in some cases it might be desirable to disable it due to performance issues.
The feature is enabled per client and can be enabled/disabled from the “Tabs” pane under Tools→Options.
You can also control it via VBA, e.g. to disable it for all users at startup:
Call ThisApplication.Database.Settings.Item("Application").Write("PreviewInspectorTabContents", 0)