Spoiler BBCode is a simple BBCode that will hide the content displaying text with the same color as the background. When you hover over with cursor, the hidden content will be revealed.
There are two formats for this BBCode:
Default, using default colors:
[spoiler]the text to hide[/spoiler]
Custom, specify colors to use:
[spoiler color="#11111" hover="#ffffff"]the text to hide[/spoiler]
Here is the screenshot from the forum topic with 3 examples for spoiler BBCode use. Second example shows the spoiler with mouse over, revealing the hidden text.
To configure default spoiler colors, open plugin BBCodes page, Defaults panel and section Spoiler has two color settings for the default BBCode colors.