`module Pen : sig ... end`

Pens: change the way lines look like in Mlpost

`module Dash : sig ... end`

Dash patterns

`type t`
`val t : ?color:Color.t -> ?pen:Pen.t -> ?dash:Dash.t -> ?scale:Num.t -> ?brush:t -> unit -> t`

`t ~color ~pen ~dash ~scale ~brush` create a brush with color `color` if TODO

`val pen : t -> Pen.t option`
`val dash : t -> Dash.t option`
`val color : t -> Color.t option`
`type brush_colored = ?pen:Pen.t -> ?dash:Dash.t -> ?scale:Num.t -> ?brush:t -> unit -> t`

Brushes with Predefined Colors

base colors

`val white : brush_colored`
`val black : brush_colored`
`val red : brush_colored`
`val blue : brush_colored`
`val green : brush_colored`
`val cyan : brush_colored`
`val yellow : brush_colored`
`val magenta : brush_colored`

#### lighter colors

`val lightred : brush_colored`
`val lightblue : brush_colored`
`val lightgreen : brush_colored`
`val lightcyan : brush_colored`
`val lightyellow : brush_colored`
`val lightmagenta : brush_colored`

#### grays

`val gray : float -> brush_colored`
`val lightgray : brush_colored`
`val mediumgray : brush_colored`
`val darkgray : brush_colored`

#### additional colors

`val orange : brush_colored`
`val purple : brush_colored`