Just thought this was an interesting article!

Here's a few excerpts:

Korean vowels have either positive or negative values. The vowels that point up or to the right are seen as positive and bright (ㅏ [a], ㅗ [o]). The ones that point down or to the left are seen as negative and dark (ㅓ [eo], ㅜ [u]).

반짝반짝 [banjjak banjjak], which uses the positive vowel sound ‘ㅏ’, expresses an image of small stars shining. On the other hand, 번쩍번쩍 [beonjjeok beonjjeok], which uses the negative vowel sound ‘ㅓ’, creates an image of big stars twinkling.

‘파랗다 [pa-lata], 노랗다 [no-lata]’ is used to express light blue and light yellow. ‘퍼렇다 [peo-leota], 누렇다 [nu-leota]’ is used to indicate dark blue and dark yellow.

This concept can also be found in the words ‘밝다 [bakda]’(bright) and ‘어둡다 [eodupda]’(dark).