I have been having a look at the letter e situation.
I opened FontCreator and opened a copy of my 10000 Outline font. The font is available on the web from the folowing link.
I then used Save As... and Tools | AutoNaming... to produce a font 10000CH2.TTF 10000 Chromatic Experiment 2 that name being 28 characters which I think may be the limit.
I then opened 10000CHR.TTF and copied the h from the previous experiment into 10000CH2.TTF.
The e glyph in 10000 Outline consists of four contours, one inside the other. From outside to inside they can be listed as follows.
1. An outer black contour.
2. A white contour.
3. A black contour.
4. A white contour.
The chromatic version for two colours needs six contours. For continuity let us regard the colours black and white carrying through and have the idea that the colour fill will be yellow.
1. An outer black contour.
2. A white contour.
3. A clockwise yellow contour.
4. A counterclockwise yellow contour.
5. A black contour.
6. A white contour.
Contour 3 is a copy of contour 2, moved in by one font unit as appropriate and its direction reversed.
Contour 4 is a copy of contour 5, moved out by one font unit as appropriate and its direction reversed.
This is a simulation so all of the contours produce black or white areas in the display. If this were a real chromatic font producing application a contour could start off as black or white and could have its colour set by the font designer using an additional choice under, say, Edit. For example, just below Edit | Change Direction could be Edit | Change Contour Colour... and then there could be a dialogue panel where the font designer could choose which colour to make the contour.
An issue which could arise could be font validation, where there could be a rule that a clockwise contour of a particular colour must either be empty or have next inside it a counterclockwise contour of the same colour.
Contours, as now, should not overlap.
A counterclockwise contour could have a clockwise contour of any colour next inside it.
Although a counterclockwise contour having a clockwise contour of the same colour both next inside it and also one font unit in from it would in effect nullify both contours it may be a good idea to allow that to happen in the font editor yet be pointed out at validation as it may be convenient during some editing operations to have that situation on a temporary basis.
I have found that a magnification of about 200% is a good balance for carrying out the one font unit movement of the additional contours, followed by a magnification of about 600% to check it.
Having produced the two additional contours, moved them and changed their directions I did a Print Screen of the image with the contours shown filled at a magnification of 61.04% (that not being critical, it is just a record of what was displayed) and pasted it into Microsoft Paint and then coloured the inner part yellow and saved it.
I then double clicked in FontCreator so as to put FontCreator into point mode and then I did a Print Screen of the new image and pasted it into Microsoft Paint and then coloured the inner part yellow and saved it.
These pictures give what seem like an impression of how the display of a chromatic font editor might look.
Finally, all of the printing glyphs except e and h were deleted and the font tested in WordPad at large sizes.
The font is available on the web.
Please note that the numbers of the contours in the theoretical discussion above do not necessarily correspond with the numbers of the contours displayed by FontCreator.
I suggested above that the colour of a contour could be chosen by Edit | Change Contour Colour... and a dialogue panel. A consideration is that that colour could either be something like foreground, background, first decoration colour, second decoration colour, third decoration colour, et cetera, thereby leaving the choice of which particular colours to use in any particular application situation to a person using a desktop publishing package which can handle chromatic fonts or that colour could be specified with red, green, blue values or Pantone values http://www.pantone.com
so that the colour choice of the font designer is passed to the desktop publishing package where it would possibly, but not necessarily, be used. Such colour choice could also be tagged with a level of firmness of choice.
For example, a two-colour font could just use foreground and first decoration colours.
For example, a holly decoration font where the letters each have green holly with red berries on them and one can select the colour of the letter as well, with a default colour of blue, could have the red, green and blue colours all specified, the blue tagged as the forground colour, the green tagged as the first decoration colour and the red tagged as the second decoration colour. The red and the green could be tagged as firm choices whereas the blue would not. So, in use in a desktop publishing package, having keyed some text, such as a display title, the text could be highlighted and a change colour dialogue panel displayed. That dialogue panel could show the colour and which formal colour (for example, first decoration colour) was which specific colour and indicate the level of firmness of the colour choice. Changing colours would usually be possible (though not always so that logos where the colour is fixed could be encoded in fonts) yet the person using the desktop publishing package could be made aware of the firmness note.
For example, with a holly decoration font, usually the green and red would not be changed, yet it would be possible in case someone were trying to produce, say, a design where the leaves are gold and the berries silver.