I ran into a similar problem with some of the light-gray buttons. Depending on your monitor’s display settings (brightness and contrast) and viewing angle (tilt), light gray can be indistinguishable from white. While I was able to readjust my colleague’s display, I can’t generally do that for customers. In that case, it’s necessary to adjust the app’s colors instead. That should include the colors on all “stock” forms such as log-in and sign-up.
This might be a matter of adjusting settings in the CSS file(s), but I’m no CSS expert.