I would like the ability to animate the colour of individual words in a block of text

I'm not sure exactly what you're trying to achieve but there are certainly ways to animate the color of individual words in a block of text.

You could add a Fill Animator on the text, and set the range of characters to adjust the color of and then keyframe that color to change over time. If you need to do more than one word with a different color, you can add additional range selectors.

Or if you just want to have different words by different colors, set the colors on the text, then dupe the layer and adjust the colors on the new layer. 

We also have scripting available for per-character color and font style adjustments if you need very specific adjustments - currently available in 24.2's beta https://community.adobe.com/t5/after-effects-beta-discussions/per-character-scripting-public-beta-announcement/td-p/14247138

There are also Animation Presets such as Fill Color Wipe, Sliding Color Flicker, Word List Highlight that could be good starting points for word/color/animation.

If I'm not understanding what you're wanting, please post back some more details, perhaps screen shots of the output you're looking for.