Update the button colours and ordering to match this:

Also, on the two column version one of the button is spilling to the next line, which looks awkward. We should prevent this OR move the "I don't know button" to a new line and have the other four buttons grouped together.

Finally can we experiment with a different selected state. Not sure what the best solution is here. Currently it is hard to see. I think that people won't often change their selection once made, so maybe the other colours could fade to grey, or the entire question box could change state? Be creative!