For color deficiencies, different lightnesses are safe e.g. dark for loss and light for gain (could be dark reds for loss and light greens for gain, but don't mix the lightnesses). Other options are icons/shapes (like up/down arrows) or pattern fills (like stripes for loss).

The general trick is you can rely on differences in color lightness, patterns, text and icons, but not differences in color hue. The page should be usable in grayscale.