There are well researched and established standards for what constitutes a minimum acceptable level of contrast in other industries, which can be applied to gaming, including system UI. Smaller text requires a higher level of contrast. For small text, a contrast ratio of 4.5:1. For large text, a ratio of 3:1.
There are good tools available to check for this, for example https://snook.ca/technical/colour_contrast/colour.html
Snook contrast checker, showing 4.4:1 colors that have enough contrast for large text, but not small
Next: High contrast mode