Suggested address list in Thunderbird unreadable

First of all, thank you: your theme has no rivals!!
Now, my (maybe stupid) question: I have the trouble wrote in the summary. The colors of the background and of the unselected items of the list are too similar and unreadable. This image shows what I mean:
http://img510.imageshack.us/img510/5214/bugt.png
Do you know if it is due on my configuration? Do you know how can I fix it? Many many thanks in any case.
Best regards

a.