Make light-grey text darker on Mac (white background)
Assuming I understand the question, the first thing I'd do is change your accessibility display settings. More specifically:


Go to Apple > System Preferences
Click on the Accessibility preference pane
Within the left-hand pane click the Display icon (it's usually the 4th one down)
Now to the right you'll see a number of checkboxes and sliders relating to accessibility display settings
Have a play with these to see if they improve the readability of light-grey text