spots
駮 centers on a pattern of contrasting spots or patches, especially on an animal's coat. The given meaning 'spots' is the core idea.
駮 combines 馬 (horse) with 交, which likely contributes the sound and may suggest a mixed or crossed pattern, giving the idea of a spotted horse.
A horse 馬 with a crossed 交 pattern on its coat: imagine a horse covered in crisscrossing spots.
For カク, picture a spotted horse wearing a cap with a cockade: cap-cock -> カク, and the horse's spots make it stand out.