I just went and checked a survey on my site and my text color is light gray as well, sorry, should have checked that first. The color is the default behavior.
If your font size is too small, you can check your browser font size setting. If that isn’t affecting your site and you still feel that the text is too tiny, it may be a CSS issue after all. There could be something overriding the default font size, but if you don’t see any evidence of customization, that probably isn’t the case. Check some other user machines and see if the font size is too small on their displays as well.