Comment 3 for bug 872572

> Ideally changing the colour of one character should
> not alter the glyph that is shown for that character.

AFAIU this is a limitation of the underlying SVG code: if changing the fill color attribute of an individual letter (or a sub-string), the differently styled character needs to be wrapped into a separate (nested) <tspan> to override the inherited style, making the individually colored character "standalone".

The same can be reproduced with any font which uses ligatures (e.g. 'Aller' or 'Lobster'):
<http://imgh.us/ligatures-ttf-inkscape-1.png>