When I get them as cut flowers for wedding work, I've noticed yellow and white are typically really fragrant, the white being a little sweeter and yellow sometimes has a spicy, peppery note. Fragrance seems less pronounced in other colors I've worked with.
A cold frame sounds ideal for them, hmmm....something I should consider. This is the time of year I'm really desperate for blooms, it would be great to have pots of fragrant freesia brightening the house!