Dallas here from the Social Care Team at Shopify.
I do see what you mean and it's odd that the text isn't appearing in the button. Before I continue can I ask you to try two things for me?
The first is to check to see if your text colors are overlapping with the same color as your button. You can see this by going into your Theme Customizer in your Store Admin (Online Store > Themes > Customize) and checking your theme colors (Theme Settings > Colors).
If these two sections are the same color then your button will just look like one blob, like this:
The other option, if the above is not the issue is that this could be a cache related issue. Have you tried clearing your cache? This helpful link gives the instructions for how to clear the cache for all browsers. Can you try that and then let me know how it works?
After that, if you're still not seeing the text please let me know the theme that you're using and if you've done any major changes to your website recently. Is it just this button that you're seeing the only button with monotone color?
I look forward to hearing back from you and working towards a solution with you.
@Dallas is right, but if you just want to change color of this button then you can follow this:
Add this css in Asset->theme.scss file at bottom
Or send me your store url so i can give exact solution.