Stroke (Both) adds color to both sides of the drawn line.

Prepare an illustration you would like to add borders to.

Open ① the Layer window, and select ② the current layer and drag over the layer that contains the image you would like to apply the filter to.

From ① the Tool Selection window, select ② Filter.

Select ① Stroke (Both).

Drag the ①Sliders to adjust the width of the borders.

Open ①Color Picker . Drag the ②Slider to adjust color.

When finished, return to the canvas with ①✓ button.

Finished.