When choosing colors take into account the contrast ratio of the foreground to the
background color. The W3C created guidelines for exactly this purpose (WCAG 2.0).
These require that text uses adequate contrast for visually impaired people.
WCAG 2.0 Level AA (standard) requires a contrast ratio of at least 4.5:1 for
normal text (14px) and 3:1 for larger text (~18px). This level represents people
with 20/40 vision (typical visual acuity of elders at roughly age 80).
While our software should be usable by people with slightly impaired vision,
we have made certain exceptions to express our brand properly while taking
into account the overall effect on the usability and accessibility of our products.
How to check the contrast ratio
The most common tool is contrast-ratio.com
where you can check the contrast ratio between two colors.