I have not found a solid correlation between red/purple stripes and quality. I don’t know that I have seen clear solid striping on seedlings (admittedly never looked specifically for them) but I usually notice it on older stems.
When growing out the Jabba’s Stash, I marked seedlings that expressed purple stems to see if they were precursors to Bubba dominance and later purpling and found that they did not show significant correlation in either dominance or later purpling. So I would be reluctant to make keeper decisions based on such early indicators.
Specifically, in regards to the Chem Kesey and Chocolate Covered Strawberries expressing the red striping, those are in their later stages (Chem Kesey is fading in the picture), so perhaps this is due to deficiency.
I have experienced the most color variation when growing under full spectrum Blurple LEDs. If any plant had even the slightest tendency to express color, it would be intensified under these LEDs. The same cuts don’t express near the color variation under White LEDs so there is something to the spectral mixing that seems to play a role in this phenomenon.