Very nice! Thanks for sharing!
Much better on the eyes 
Edit: Is there a way to make quoted strings "" have a different colour than variables?
Edit2: Also, how can I change the background colour of braces and parentheses when the caret is beside them (I want to replace the default white by a light gray)?
Edit3: How can I make the style take effect only for ahk documents? Right now I have a gray/black background for all documents (giving weird lexing for xml documents for example).
1: View --> User Define Dialog... Variables are set in the 3rd Group section of the Keyword Lists tab, and strings in the Delimiter 1 section of the Operators tab. This dialog, BTW, writes to the userDefineLang.xml file.
2: Settings --> Style Configurator, Global Styles, Brace highlight style. This dialog writes to stylers.xml.
3: Bad news. Because AHK is a user defined language instead of a built-in language, it can't be selected in the Languages list in the Style Configurator, and from what I can tell, the only way to change the items for AHK is to change the Global Styles language - which applies globally, including xml, html etc.

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One option is to go to Global Styles, Global Override in the Configurator, check "Global background color", and set the background color to R/G/B = 31/31/31, which matches the background in entropic’s theme. This will set a dark background for all elements of all languages. The downside to this is that some of the text colors used for these other languages may not look good against this background – for example, the blue tag names in XML. To fix that, you’d need to tweak the colors of each language you plan on using, via the Style Configurator - select the appropriate language, then the elements defined for that language.
If anyone knows any easier ways, please let us know

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