This window is where you adjust the text settings for a block of text on the invoice, which is an option accessible from the Options ~ Page Styles page.

Font:

Select the font face for the text.

Size:

Select the font size for the text.

Style:

Select if the text should be bold or italicized.

Color:

Click inside the color box to select a new text color.

Alignment:

Select right, center or left alignment for the text.