There are numerous aspects involved - from the more obvious points you highlighted - to the deeper aspects relating to our own energy body (chakra system). In the case of MKUltra, it appears that the colours are being embedded in children's minds and associated with particular ideas for later recall. If you watch the video at the end of first video in my post, you can see the decoded message on twitter which assigns certain programs to the colours that keep being used in all of these dodgy videos on youtube.

I have made a few posts on colours before. This is maybe the main one:

https://steemit.com/psychology/@ura-soul/colours-in-society-are-extensive-covert-mind-control-systems-being-applied-to-us-all

Another relevant post is here:

https://steemit.com/life/@ura-soul/slave-no-more-series-tips-for-liberation-of-the-earth-heart-or-3-the-mind-control-used-by-shops-is-far-more-evil-than-most-have

Colours transcend more recently evolved brain functions - they are like a keypass into the unconscious self.