As noted by ms4py, what you need is a Color Scheme. Sublime Text (and ST2) use the old format supplied by TextMate, .tmTheme. Basically it's an xml document with specific markup.
Check the application menu "Preferences" > "Browse Packages" and a Finder window will pop up to Sublime's packages folder. There you'll find the folder "Color Scheme - Default" which contains your installed default themes, including iPlastic.tmTheme.
Simply open the file in a text editor (ST will do just fine ;) ) and change the parts you want to adapt, e.g. to change your "Keywords" style find:
<dict>
<key>name</key>
<string>Keyword</string>
<key>scope</key>
<string>keyword</string>
<key>settings</key>
<dict>
<key>foreground</key>
<string>#0000FF</string>
</dict>
</dict>
and adjust the foreground color (#0000FF in this case) to your liking.
You can find other supported attributes throughout the file, e.g. foreground, background or fontStyle.