The only way I've found to change colors is to edit the following three files in whatever theme I'm using.

/usr/share/themes/{theme name}/gtk-3.0/gtk.css  

/usr/share/themes/{theme name}/gtk-3.0/settings.ini  

/usr/share/themes/{theme name}/gtk-2.0/gtkrc

In the beginning of these files you'll find 4 pairs of core foreground and background colors used in applications based on the gtk 2 and gtk 3 libraries. Pair base_color and text_color are used for the document or text entry portions of windows where bg_color and fg_color are are used for the windows area where icons and labels are displayed.

Selected pair is for selected text and the tooltip pair is used for the tips that pop up when you hover over a button or link. These colors may be applied by applications with varying opacity or shadings. The colors you'll want to check are the base_color and text_color pair. #ffffff is pure white. You may find the gcolor2 application helpful for determining the color codes. These sets of labels appear in all three files so I've been changing all three to be the same for any label I change.

Here's an example of what I changed in the gtk.css file in the Ambiance theme:

Keep in mind that the ones you're most interested in are base_color for background and text_color for the text foreground. I your example they both appear to be the same, #ffffff or other tinted white colors.

/* default color scheme */  

@define-color bg_color #cdc3b8;  

@define-color fg_color #262626;  

@define-color base_color #accdff;  

@define-color text_color #262626;  

@define-color selected_bg_color #01b9fc;  

@define-color selected_fg_color #ffffff;  

@define-color tooltip_bg_color #A3D0FF;  

@define-color tooltip_fg_color #023C79;