mbbill/undotree — pull request #11 by inkarkat (2012-11-28 10:10:22+00:00)
Title: Allow customization of syntax highlighting.

By using :hi def link instead of :hi def, it is possible to predefine syntax overrides in one's .vimrc. Undotree will only set the highlighting for items that haven't yet been defined.

PS: My customizations are:
highlight link UndotreeBranch Normal
highlight link UndotreeNode Normal
highlight link UndotreeSeq Constant