Given two vowel phonemes that contrast by length alone, will their phonetic realizations typically have different vowel qualities?
For example, if a language has two vowel phonemes, /ɑ:/ and /ɑ/, would they be realized as [vowel sound 1] and [vowel sound 2]-- in other words, as vowel sounds that differ by features in addition to length?
If so, what are some common long vs. short phonetic realizations in languages that have phonemic long vs. short vowels?