Ben – will be happy to help. The first query is not clear to me – are you asking how to set that thumbnail for a blog post or is it that you want to rearrange the thumbnail, titles?
For setting a thumbnail for a portfolio or a blog post, just set the featured image as shown below in the blog post edit or portfolio edit window –
For changing the order of the thumbnail, titles, you will need to edit the file
For the second query, you can change the hover color for thumbnails in portfolio and blog by inserting the following CSS into Custom CSS tab in the Theme Options panel or the
background: rgba(70, 165, 213, 0.8);
In case you need it, more information about rgba syntax here – http://shapeshed.com/css3_tour-rgba_colour_values/