Built-in

The default 'blank' presentation actually contains 12 different colour schemes.
You can quickly see how many colour schemes a presentation has by displaying the Slide Design task pane.
Select (Format > Slide Design) and then choose the Color Schemes link at the top.
This presentation contains 12 colour schemes. The default colour scheme is the one in the top left corner.

Default Colour Scheme

You can display the actual colours used in each colour scheme by using the Edit Color Schemes link at the bottom of the task pane.
Highlight the colour scheme you are interested in (in this case top left) and select Edit Color Schemes.
The Custom tab is displayed initially and displays the corresponding colour scheme.
This is the default colour scheme used when you create a blank presentation.
The Standard tab lets you manage the colour schemes and is discussed later.

Background - Used for the slide background
Text and Lines - Used for any text except the presentation title and slide titles. This is usually a colour that contrasts with the background colour.
Shadows - Used to produce shadow effects for objects drawn on the slide. Normally a darker version of the background colour (unless the background colour is very dark).
Title Text - Used for the presentation subtitle and bullet text. This should contrast with the background colour. This colour should complement the text and lines colour.
Fills - Used as the default colour for any objects or shapes.
Accent - Used for templates that use accent colours.
Accent and hyperlink - Used as another accent colour. This colour is also used to display hyperlinks that have not been followed. This colour is also the default colours for charts created with Microsoft Graph
Accent and followed hyperlink - Used as another accent colour. This colour is used to display hyperlinks that have been followed.

Changing the Scheme Colours

You can easily customise a colour scheme by editing the individual colours.
Click on the small coloured block on the left and select Change Color.
This will display the familiar colour picker dialog box.
When you have finished changing the colours select Apply to apply this colour scheme to all the slides.

Example Text Slide

This slide shows what the default text slide looks like.
This illustrates where each of the eight colours are used. Note that the background is white.

Example Title Slide

This slide shows what the default title slide looks like.

Important

PowerPoint has built-in colour schemes that make it easy for anyone to create great looking slides.