This is easily done by adding to your custom CSS file, assuming you know the class of the elements you want to modify. In Hueman, the elements on the sidebars have classes assigned as follows:
.widget_recent_entries or widget_recent_comments or widget_archive, widget_categories, widget_meta etc.
Use the element inspector in your browser to inspect each element and grab that class.
You can then simply change the attibutes of the whole div, just the <H3> element or any of the sub-elements in the DIV by adding a line to your custom CSS.
For example:
.widget_recent_entries { background-color: #b0c4de;}
.widget_recent_entries > H3 { background-color: #ffffff;}
The first line will change the entire ‘recent entries’ section’s background color.
The second line will change just the title of the ‘recent entries’ section to have a white background.
Hope this helps.