Inversion Mode: Toggles ellipse tool's inversion mode on/off. When inversion is OFF, the ellipse's border will always be drawn in the fore-ground color and filling (for filled ellipses) will always be done with background color. When inversion is ON, the ellipse's border will appear in fore-ground color over the areas originally painted in background color and in background color over the areas originally painted with non-background color. The color for the "filling" (when enabled) will be exactly opposite.

Solid Ellipse: Creates an ellipse filled with fore-ground color (+ inversion mode effect is applied with enabled).

Filled Ellipse: Creates an ellipse with the border of fore-ground color and filled with the background color (+ inversion mode effect is applied with enabled).

Unfilled Ellipse: Creates an ellipse with the border of fore-ground color and no filling (+ inversion mode effect is applied with enabled).

Size: Border width (irrelevant for solid ellipses).