Color Task 1
Color can be used to draw the eye to a given place on the screen.
Here the word eu is colored differently from the main body of the text. The point of gaze is involuntarily drawn to it.
Color Task 2
Color can be used to block related text, i.e. to connect into a perceived unity a collection of geometrically disconnected words scattered throughout the text.
Here every word ending in t is colored green. The result gives the illusion of looking at a single green object imperfectly seen through "holes" in the grey text.
This may be a wilderness survival mechanism: a tiger still looks like a tiger even though its image on your retina is split up (by leaves and branches) into disconnected parts.
Color Task 3
If color is overused, then it becomes less useful for supporting either task 1 or 2.
Here although the word eu is colored red as before (Task 1), many other words are colored. Even though red is used for just this one word, the eye is no longer drawn to it so compellingly. Nor is the blocking effect of Task 2 quite so apparent.