Options > Colors… opens one dialog for all the colors of the comparison panes. Each row is one kind of line, with a swatch for its text color and one for its background:
| Normal | lines that are the same on both sides |
| Difference | lines that differ |
| Inline difference | the changed part inside a different line (see Show Inline Differences) |
| Modified | lines you edited in this session |
Click a swatch to open the Windows color picker for that color. The Preview box shows sample lines in the current screen font and follows every change immediately. Nothing is applied to the comparison until you press OK; Cancel leaves the colors as they were.
The Contrast column shows the contrast ratio between text and background of each pair, as defined by the WCAG accessibility guidelines. A pair below 4.5 : 1, the ratio recommended for running text, is flagged, and the line under the table names the pairs concerned. This is a hint, not a lock: you can apply such a combination anyway. The factory setting for the inline difference, red on yellow, is itself below the line (3.7 : 1) — it is carried by the hue rather than by brightness, and it is kept that way on purpose.
A preset only fills the editor; press OK to apply it.