I wouldn't mention it, except that Thunar is the default file manager and Mint-Y is, obviously, a Mint theme. So this unreadable text is, in a sense, default behaviour.
EDIT: The XFCE-Dusk theme is similar to Mint-Y but produces a banner that is considerably - but still not perfectly - readable.
Please see the image below.
I wouldn't mention it, except that Thunar is the default file manager and Mint-Y is, obviously, a Mint theme. So this unreadable text is, in a sense, default behaviour.
EDIT: The XFCE-Dusk theme is similar to Mint-Y but produces a banner that is considerably - but still not perfectly - readable.