Incorrect Coloring of Search Field with "High Contrast" accessibility enabled

[evacks]

The "High Contrast" accessibility setting works properly but there appears to be an error in the way the search field is colored - I tried typing in it but I can't read the letters. Tested in the latest noble numbat

Edit: Confirmed the issue on Mantic Minotaur too

I happily remain at your disposal for any further information - I wasn't sure if this was a launchpad-appropriate bug so I filed it here directly