| oBox | Data.GraphViz.Attributes, Data.GraphViz |
| Octagon | Data.GraphViz.Attributes.Complete, Data.GraphViz.Attributes, Data.GraphViz |
| oDiamond | Data.GraphViz.Attributes, Data.GraphViz |
| oDot | Data.GraphViz.Attributes, Data.GraphViz |
| OldLace | |
| 1 (Data Constructor) | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| 2 (Data Constructor) | Data.GraphViz.Attributes.Colors.SVG |
| Olive | Data.GraphViz.Attributes.Colors.SVG |
| OliveDrab | |
| 1 (Data Constructor) | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| 2 (Data Constructor) | Data.GraphViz.Attributes.Colors.SVG |
| OliveDrab1 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OliveDrab2 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OliveDrab3 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OliveDrab4 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| oneOf | Data.GraphViz.Parsing |
| oneOf' | Data.GraphViz.Parsing |
| onFail | Data.GraphViz.Parsing |
| onlyBool | Data.GraphViz.Parsing |
| OpenArrow | Data.GraphViz.Attributes.Complete |
| openMod | Data.GraphViz.Attributes.Complete |
| optional | Data.GraphViz.Parsing |
| optionalQuoted | Data.GraphViz.Parsing |
| optionalQuotedString | Data.GraphViz.Parsing |
| Orange | |
| 1 (Data Constructor) | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| 2 (Data Constructor) | Data.GraphViz.Attributes.Colors.SVG |
| Orange1 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Orange2 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Orange3 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Orange4 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OrangeRed | |
| 1 (Data Constructor) | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| 2 (Data Constructor) | Data.GraphViz.Attributes.Colors.SVG |
| OrangeRed1 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OrangeRed2 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OrangeRed3 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| OrangeRed4 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Oranges | Data.GraphViz.Attributes.Colors.Brewer |
| Orchid | |
| 1 (Data Constructor) | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| 2 (Data Constructor) | Data.GraphViz.Attributes.Colors.SVG |
| Orchid1 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Orchid2 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Orchid3 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Orchid4 | Data.GraphViz.Attributes.Colors.X11, Data.GraphViz.Attributes, Data.GraphViz |
| Order | Data.GraphViz.Attributes.Complete, Data.GraphViz.Attributes, Data.GraphViz |
| Ordering | Data.GraphViz.Attributes.Complete |
| ordering | Data.GraphViz.Attributes, Data.GraphViz |
| Orientation | Data.GraphViz.Attributes.Complete |
| orQuote | Data.GraphViz.Parsing |
| Orrd | Data.GraphViz.Attributes.Colors.Brewer |
| Ortho | Data.GraphViz.Attributes.Complete |
| Osage | Data.GraphViz.Attributes.Complete, Data.GraphViz.Commands, Data.GraphViz |
| OutEdges | Data.GraphViz.Attributes.Complete, Data.GraphViz.Attributes, Data.GraphViz |
| OutputMode | Data.GraphViz.Attributes.Complete |
| OutputOrder | Data.GraphViz.Attributes.Complete |
| Overlap | |
| 1 (Type/Class) | Data.GraphViz.Attributes.Complete |
| 2 (Data Constructor) | Data.GraphViz.Attributes.Complete |
| OverlapScaling | Data.GraphViz.Attributes.Complete |
| OverlapShrink | Data.GraphViz.Attributes.Complete |
| Overline | Data.GraphViz.Attributes.HTML |