Add different colors to each text character in a text box.
Now you can style individual characters within a text box. To apply multi-colored text to a text box, select the text box then highlight each character one at a time either on the artboard or in the Text Editor box and use the Color Picker to choose the color you want for each individual character as they are highlighted.
Please note that the color selections will disappear when that text is edited. You are also not able to have multi-colored text when using the Curve Text Feature.