It's become a part of my way of working that I check areas of my design are adhering to accessibility guidelines, WCAG2.0 colour contrast in particular.
At the moment I'm working on creating a new colour palette. The primary colours i'm experimenting with are relatively saturated (#25AB2B as an example).
I'm noticing that these saturated colours for 'calls to action' (buttons) typically have to be paired with a dark text colour (black for instance) to meet/exceed the contrast ratio guideline of 4.5:1...
Text size for these buttons wouldn't exceed 16px.
I'm finding examples where these sorts of colours are constantly being paired with light foreground/text colours for buttons, Spotify for example (who make mention of their green 'optimised for accessibility' but still fall even shorter of the guidelines than my example above) .
My question is...
I'm trying to understand if there are any design / human vision / phycological considerations that are contributing to my very subjective opinion that the black text on bright / saturated background is actually less readable (for me), despite having a much higher contrast ratio. Is there anything I'm not taking into account, or should I just trust the numbers?