Google Docs is currently experiments a new interfaces for the document editor and Spreadsheets.
Inspired by Google's multi-month UI refreshing project based on the Google+ interfaces - the new UI remove all the colors from the icons and other UI elements, remove the Google Docs logo, add new scrollbars and a "Collaborate" menu that includes all the features from the "Share" drop-down.
Unlike the new interfaces for Gmail and Google Calendar, the updated Google Docs apps don't use too much whitespace. You can switch to the new interfaces by clicking "Try now" in a small message that announces the changes when you open a Google Docs document or spreadsheet.
To go back to the old UI, choose "Use the classic look" from the "Help" menu.
In other related news, Google Sites also tests a new UI:
Also, note that Google Calendar has now sarted separating old events from upcoming events: old events are now grayed out. The interface also grays out future recurring events (this was an experimental feature in Google Calendar Labs).
To disable the new features, just go to the "Options" menu from Google Calendar's navigation bar, select "Calendar settings", go to the "Event dimming" section and disable these two options: "Dim past events" and "Dim recurring future events".
Google says that the brightness of these events is reduced "so you can focus on today", although you'll be able to better focus on the future, as well.