Fortunately, there are two ways to dress up your Microsoft Word document with rainbow text. Apply a rainbow color gradient to any text in your document by changing the font color settings, or use WordArt to create a rainbow text "picture" with multiple options for tweaking the rainbow colors and text formatting.
Select the text in your document that should appear in rainbow colors. On the Home tab, in the Font group, click the down arrow next to the font color icon and click "Gradient," with the color gradient icon, and then select "More Gradients." A Format Text Effects panel opens that allows you to customize the gradient.
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Formatting Text Effects
On the Format Text Effects panel, select the "Gradient fill" radio button. You can choose a preset gradient, although these use only two colors. (In Word 2010 only, you can also choose one of two rainbow gradient presets.) For a rainbow gradient in Word 2013, click each slider on the color bar in the Gradient stops section and select a custom color using the Color icon. You can also adjust the width of each color section and add or subtract sliders to change the number of colors. You'll see each setting applied in real time on your selected text. Each color can also be adjusted for transparency and brightness below the Gradient stops section.
Go to the Insert tab on the ribbon and click WordArt in the Text group to insert WordArt into your document. The Drawing Tools Format tab will appear on the ribbon. Click the down arrow next to Shape Fill in the Shape Styles group, click "Gradients," and then click "More Gradients" to open a Format Shape panel. This panel is similar to the Format Text Effects panel described above, and the gradient can be customized the same way.
You can also shape your WordArt like a rainbow. To do this, click the Text Effects icon in the WordArt Styles group on the Drawing Tools Format tab, and choose a rainbow shape from the Transform option on the menu. Word offers several options for changing this shape, accessible by right-clicking the WordArt and clicking on "Format Shape." You can also click and drag the corners of the WordArt box to change the arc of your rainbow.
Compatibility Mode Issues
Gradient text effects and customized WordArt gradients are available only in Microsoft Word 2010 and later versions. These features are not available in Office Online. If you are using Word 2010 or later and the gradient options are grayed out, Word is operating in Compatibility Mode. To disable Compatibility Mode on your current document only and enable gradient text effects, click "File" and then click "Convert."