To set an annotation style property such as color, interior color, border style, padding, etc to an annotation.

doc = PDFDoc(filename)
page = doc.GetPage(1)

circle=Circle.Create(doc.GetSDFDoc(), Rect( 100, 100, 200, 200 ))
circle.SetColor(ColorPt(0, 1, 0), 3)
circle.SetInteriorColor(ColorPt(0, 0, 1), 3)
circle.SetBorderStyle( BorderStyle( BorderStyle.e_dashed, 3, 0, 0, [2, 4] ) )
circle.SetPadding( 2 )
circle.RefreshAppearance()
page.AnnotPushBack(circle)

Add or edit PDF annotations sample
Full code sample which shows how to add or edit PDF annotations (e.g. hyperlink, intra-document link, stamp, rubber stamp, file attachment, sound, text, free-text, line, circle, square, polygon, polyline, highlight, squiggly, caret, and ink).