Finding And Replacing A Line

Say I have some CSS, which is several hundred lines long, with the
contents in this format:

..foo {
blah
color:#000;
blah
}
..bar {
blah
color:#FFF;
}

where the selectors and their opening braces, their closing braces, and
declarations are each on their own lines (always), how can I replace a
specific declaration (line) given a unique selector and a declaration
property. For example, if I wanted the 'color' declaration property line
in the 'bar' class changed.

At the moment I'm iterating through the CSS one line at a time looking
for the selector and then looking for the declaration property (before I
hit the closing brace).