How to edit theme colors in TextMate 2?

In TextMate 1 there is a Fonts & Colors tab in Preferences to edit theme colors, but in TextMate 2 I cannot find how to do the same...

I can select a theme in the View menu, but I want to customize a theme, the same way it was possible in TextMate 1, by selecting the "scope" and changing the color with a palette and the font style.

Where is this function in TextMate 2?

Option 1: use TextMate 1:

open ~/Library/Application\ Support/Avian/Bundles/Themes.tmbundle/Themes/Custom.tmTheme -a TextMate
cp ~/Library/Application\ Support/TextMate/Themes/Custom.tmTheme \
~/Library/Application\ Support/Avian/Bundles/Themes.tmbundle/Themes/Custom.tmTheme

Option 2: edit the theme as an old-style plist from the bundle editor:

Option 3: edit the tmTheme file directly by opening it with mate:

mate ~/Library/Application\ Support/Avian/Bundles/Themes.tmbundle/Themes/Custom.tmTheme

The last two options require you to close and reopen files to make them use the edited theme. tell app "TextMate 2" to reload bundles does not work.

You can use pl and plutil to convert between the XML and old style formats:

pl -input file.plist -output file.plist
plutil -convert xml1 file.plist

Theme tweaking of the type you could do in TextMate 1 is not yet featured in TextMate 2 itself. HOWEVER... I just came across this very cool online TextMate theme editor. Its interface imitates the Fonts & Colors tab in the TM1 preferences. It apparently only works in Chrome, but I use Chrome anyway so I'm off to play with it.