Create PDF file with Spot Colors

Further investigation seems to indicate that the Apple Core Graphics API does not natively support the Separation color space (as defined by Adobe) but it does support DeviceN color spaces - or Color Models. DeviceN color spaces support Spot colors so this seems like an option for us to use. However it is still unclear how one would create such a DeviceN color space.

[% Define the color space to be DeviceN
    /DeviceN
    [/Ruby /Emerald /Sapphire /Turquoise
    /Amethyst /Citrine]
    /DeviceRGB
    {%define new values and clip to 1.0
      6 -1 roll 1 index add 2 index add
      6 -1 roll 2 index add 4 index add
      6 3 roll add add 4 -1 roll pop
      3 -1 roll dup 1 gt {pop 1} if
      3 -1 roll dup 1 gt {pop 1} if
      3 -1 roll dup 1 gt {pop 1} if
    }
] setcolorspace

I did find this pseudo code for C# which seems to shed some light on it.

> Spot color can be represented in PDF using 'Separation' or 'DeviceN'
> color spaces.
>
> A separation color space can be treated similarly to grayscale color
> space. For details on separation color space, please refer to section
> 4.5.5 'Special Color Spaces' in PDF Reference Manual
> (http://www.pdftron.com/downloads/PDFReference16.pdf).
>
> The following C# pseudocode can be used to create a separation color
> space based on a PostScript function:
>
> static ColorSpace CreateSpotColorSpace(PDFDoc doc)
> {
>   Obj sep_cs = doc.CreateIndirectArray();
>
>   sep_cs.PushBackName("Separation");
>   sep_cs.PushBackName("LogoGreen");  // The name of the colorant
>   sep_cs.PushBackName("DeviceCMYK"); // Alternate color space
>
> // Create tint function (using PostScript calculator function).
> // Tint function is used to transform a tint value into color
> // component values in the alternate color space.
> string ps_funct = "{ dup 0.84 mul exch 0.00 exch dup 0.44 mul exch
> 0.21 mul }";
>   Obj tint_funct = doc.CreateIndirectStream(new
> System.Text.UTF8Encoding().GetBytes(ps_funct));
>   tint_funct.PutNumber("FunctionType", 4);
>
>   Obj tint_domain = tint_funct.PutArray("Domain");
>   tint_domain.PushBackNumber(0);  // Gray
>   tint_domain.PushBackNumber(1);
>
>   Obj tint_range = tint_funct.PutArray("Range");
>   tint_range.PushBackNumber(0); // C
>   tint_range.PushBackNumber(1);
>   tint_range.PushBackNumber(0); // M
>   tint_range.PushBackNumber(1);
>   tint_range.PushBackNumber(0); // Y
>   tint_range.PushBackNumber(1);
>   tint_range.PushBackNumber(0); // K
>   tint_range.PushBackNumber(1);
>
>   sep_cs.PushBack(tint_funct);
>   return new ColorSpace(sep_cs);
>
> }

So how would one define such a DeviceN color space using the Core Graphics API ?

I am assuming that one should be able to define this using a CFPropertyList and then use the CGColorSpace(propertyListPlist: CFPropertyList) API to do so.

Any help would be appreciated.