Most decorators have a certain style or taste that they like to work within, which sometimes means it can be difficult for them to break out of the norm if you're requesting a style that they aren't used to.
Before you hire a decorator, make sure to check out several candidates' portfolios to see what style parameters they're used to working within, and go with the decorator who best showcases what you want to see in your home. If you're after a cozy living room done in whites, be wary of choosing the designer who has color plastered all over her portfolio.
And if the decorator in question is absolutely sure that she can give you what you want -- even if her portfolio doesn't illustrate it -- ask for proof that she can get the job done to your satisfaction. Request references from previous clients, or insist that a clause be put in your contract to ensure that the job is done to your liking.