Korean has an interesting feature, in that mimetic words and colours can be altered by changing their vowels from one vowel harmony grouping to the other. The two groupings are called yin vowels and yang vowels, and in mimetic words, the yin vowels (ㅓ[ʌ], ㅜ[u], etc.) carry semantic shades of "dark/impure/big", while yang vowels carry shades of "bright/clean/small". By switching from one to another, you can change the meaning slightly.
For example, "꿀꺽" (ggulggeok) and "꼴깍" (ggolggak) both mean "the sound of gulping" (they are mimetic adverbs), but the first indicates larger gulping than the second one.
Are there any other languages where vowel harmony can be used semantically like this, rather than just phonologically?
(I should note that vowel harmony isn't restricted to this in Korean; it is also used in the usual way, with some suffixes harmonizing with the vowel of the last syllable of the root).