You can hide the gray line from the header area in the Blaskan theme with CSS like this:
Or you could add a line that looks like the one at the top of http://theagencymodels.com.au/blog/ by copying the CSS from that blog and changing the selector to "#header-message" like this:
border-top: 1px solid #EAEAEA;
border-bottom: 1px solid #EAEAEA;
Note that the line below the header text on http://theagencymodels.com.au/blog/ is really the navigation area and if that was filled in then it would change the look. Same goes for the "#header-message" area on http://pavementportraits.com/ If you add a tagline, it will change the look of the line.