Yansıttıkları, geçirdikleri veya yaydıkları ışıktan kaynaklanan ve bu ışığın dalga boyuna bağlı olarak görsel bir duyuma neden olması ile ilişkili, cisimlerin bir niteliği.
สี คือการรับรู้ความถี่ ของแสง ในทำนองเดียวกันกับที่ระดับเสียง