OmniFocus 2.5 for Mac
In OmniFocus Preferences you’ll see a brand new pane: Style. Inside are both font collections and color palettes. Along with the ability to create your own styles, we’ve included some good-looking pre-made sets.
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If you’re wanting to create your own color palette or font collection, check out this support article for more about what’s involved. Be aware! There are a lot of colors involved—it might be a productivity-breaker!
It’s not just fonts and colors. There are a ton of constants for controlling the spacing and padding. There’s also an OmniFocusColors app to make it easier to edit the property list file.
Update (2016-04-10): Nicholas Riley:
OmniFocus 2.5 finally letting me migrate from v1. Some niggles remain, but… (compare …)