To change the actual editors theme:

If you have http://www.greasespot.net/ installed the link below should enable Ambiance on HyperDev:
(I think Ambiance fits best)
https://gist.github.com/qk4/dc2c4517c93d86a0d2c8fa97a1781ae5/raw/6a23966f99419fa8df2af09ae9dcf7e2f8ba44ab/ambiance_theme_for_hyperdev_editor.user.js

Lots of people like Monokai though:
https://gist.github.com/qk4/159b11a4ebd89b5cbf087a61689cc400/raw/dea487f0d0707daeb3c580d41112b7908d5b071a/monokai_theme_for_hyperdev_editor.user.js

And you could just edit it through the greasemonkey script manager and easily change the theme it sets if you want a different one.

https://github.com/ajaxorg/ace/tree/master/lib/ace/theme

If you'd like to improve it, or have done so for yourself, please leave the changes as a comment below and I'll update it (and credit you).
Or send a pull request https://github.com/qk4/userstyles

If you've made/found a better dark style for Hyper Dev let me know! I started this one because I found none.