Dark paint on white grout

[chocatoo]

My DH painted the bathroom wall a darkish denimy blue (which I am v happy with!), however the paint has kind of bled into the white grout around the tiles at the corners and sides which looks horrible.
Can anyone offer ideas of how to remove it from the grout or disguise it? I wondered about a grout pen?

I found a fab grout paint pen at Homebase which worked wonders. Go for it!