If you spend all day in spreadsheets, sooner or later you want something to help you spot what's important or different. The motion study expert Frank Gilbreth told factories to paint parts different colors to help factory workers spot the right pieces more quickly; Calc has roughly equivalent features to help point out the different types of data you're working with.
Many of the settings are controlled here. Choose Tools > Options > OpenOffice.org Calc > General. Click the image to see it bigger.