In the new Discovery Channel National Parks placemark collection I noticed they had colored description bubbles in Google Earth. So, I set out to figure out how they did it in the KML. It turns out you need the following KML tags added to a placemark KML file:
- <Style> – name a style type using the “id” parameter
- <BalloonStyle> – start a style for the Balloon
- <color> – specify a color
- <StyleURL> – specify the Style for a specific balloon.
You need the corresponding closing tag for each of the tags above. Read the documentation on KML here.
You can see an example placemark 
I placed in the big blue ocean, and here’s the source (the important parts are highlighted in the color red):
<?xml version="1.0" encoding="UTF-8"?> <kml xmlns="http://earth.google.com/kml/2.0"> <Document> <Style id="bigblue"> <BalloonStyle> <color>ffa56a</color> </BalloonStyle> </Style> <Placemark> <name>The Ocean</name> <description>This is the big blue Atlantic Ocean.</description> <LookAt id="khLookAt714"> <longitude>-42.26486304831379</longitude> <latitude>22.39966410949204</latitude> <range>628332.929568931</range> <tilt>0.0</tilt> <heading>0.0</heading> </LookAt> <styleUrl>#bigblue</styleUrl> <Point id="khPoint715"> <coordinates>-42.4724104803559,24.20421380978096,0</coordinates> </Point> </Placemark> </Document> </kml>
