Ensure snapshots have white backgrounds.
Ensure snapshots have white backgrounds.

Fixes the last bit of [#59358426], I hope. By setting the background color as well as the image, we prevent the theme background from showing in the snapshot.

https://www.pivotaltracker.com/story/show/59358426
concord-consortium/lara,concord-consortium/lara,concord-consortium/lara,concord-consortium/lara,concord-consortium/lara