Can being blonde still look professional?

I work in a professional atmosphere where I need to be taken seriously. I'm 25 which is very young for the profession I'm in. Should I stick to darker shades to look more professional and so clients don't think they are dealing with a young, inexperienced child? My natural color is a light, mousy brown at the roots with lighter blonde tips. I like being darker but also don't want to look like...unapproachable.