[twitter-dev] question with twitter color design

[爵溪]

hi,all
In twitter's 'setting' we can choose 5 colors (background, text,
links, sidebar, sidebar border),but i notice that links in the sidebar
have a hover background color( just like white+sidebar background
color ) ,which is not from the 5 colors i metioned above and not
privided by the api .
any idea how to calculate this color?