Could it be of interest that the Arabic letter names ka:f and qa:f have
prescribed pronunciations with very different vowels, ka:f having the long
counterpart of Eng. man (which actually is long in most varieties of
English), while qa:f has the vowel of Eng. call or crawl? Great variation
is expected in systems with few phonemes.

Jens

[Sergei asked:]

> What are the typological grounds for the statement that uvulars
> trigger a-colouring (and not o-colouring, for instance)? What would
> be a possible (neuro)physiological explanation? Just wondering.