Slacy, I am not aware of a direct way to mix colors in a single block of text in Vegas. Some people use 3rd party titling software like BluffTitler to supplement Vegas' limited titling capabilities.

Here is a Vegas workaround that might do for your needs.
1. Create your text event and then duplicate that text event into a new track directly above your original text event.
2. Place your timeline cursor somewhere in the middle of the text event so you see the text in your preview window, then open the duplicated text event.
3. Change the color of the duped text to the color you want for the individual word.
4. Delete all the duped text except for the word you want to be the new color, then use the placement tool to move the colored word directly over the original word in the lower track.

This will give you a "single" block of text with one word in a different color. Now, what if you want to animate this text (e.g., zoom in on the text block)? You don't want to have to manually synchronize pan/crop on both events. Simply create a new controller track above your two text tracks, and make the text tracks child tracks to the controller. Now use the controller's track motion to control movement of the two text events simultaneously.

Hope this helps,
Jerry