My light gray helper text looked great on my monitor until I tested it on a cheap laptop
I spent 3 hours tweaking a form design last Friday where the helper text was #999 on white and it looked totally fine on my calibrated screen. Then I pulled it up on my old work laptop and the gray basically vanished into the background, so I bumped it to #666 and finally passed the checker. Do you test your text against the background color first or just eyeball it and hope for the best?