It appears that GTK's integrated "Search-as-you-type" has a bug (this is the Rhythmbox bug I filed right now). I've seen it in many places around the gnome desktop.
See the bug below for a screenie.
The problem: White is the color for dark themes' text. When the search bar changes, it should either force the text to be black, change the color of the yellow, or detect the lightness and if it's too light, change the text.