Editor color

Depends what your editor is but I'd imagine you can.

In Sublime, Go to Preferences > Color Scheme

Additional color schemes for Sublime here: http://colorsublime.com/

I mean to get through the challenges

I don't believe there is currently a way to customize the challenge workspaces but I can definitely see where it has some accessibility issues, particularly with php block tags which are an olive color that doesn't contrast well with the background.

I'd submit a request to help@teamtreehouse.com and see if they would be willing to implement a setting for users to modify these colors. I don't see any reason why it wouldn't be a feature that more people would want.

As for a temporary work around, you could use a plugin for your browser such as https://chrome.google.com/webstore/detail/stylebot/oiaejidbmkiecgbjeifoejpgmdaleoha?hl=en Stylebot which lets you override a websites styles with your own. I know it isn't ideal nor should it have to be up to a user to fix an issue like this, but at least it will make things easier until there is a better solution.