Thanks for your question and thanks for using Callaway WordPress theme with BoldGrid Post and Page Builder !
With the Callaway theme you control your theme color from the Color Palletes section of the Customizer Appearance<<Customize<<Colors. Each portion of the color palette controls different elements of your theme. You would need to find the color the corresponds with your blog post widget text and you can change it here.
If you want to select the blog post widget element more specifically you can do so using CSS. You would need to find the CSS class selector or class ID for the blog post widget and change it using Appearance<<Advanced<<Custom JS and CSS.
Our Callaway theme is considered one of our legacy themes and is no longer fully supported. If you would like a fully customizable solution you might want to consider our Crio Pro WordPress theme. Crio has over 400 premium features including full color customization control. With Crio you can edit every detail of your theme down to the letter. It would definitely help speed up and simplify your design process.
I hope you find this information helpful. Let us know if there is anything else we can assist you with.