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.
Here's what it looks like when, in the Display section of the Options window, you mark the Formulas option.
Here's what it looks like when you mark Shown References in Color. It means if you double-click a formula, the referenced cells are shown color coded.
And if you mark the Value Highlighting option, then formulas are shown in a different color than formulas.
And in the same options window on the left side, you can change the color of the borders between the cells from light gray to whatever you want. Here's what they look like in magenta.
Tracing precedents means, for the selected cell or cells, show other cells that are a step up in the calculation. For instance, the tax rate is used in the selected cell to figure out after tax monthly income, so it's a precedent.
And, if you've got some errors, the Trace Errors feature will show what other cells are involved in the error cell.