Whether you use the color on a wall, in a pillow or to add a pop of color to your bathroom vanity...I think it can be both classy and modern. Use some navy paint against white molding and boy the contrast is fabulous!
See for yourself.....
Some of my favorite Dark Blue Paint Colors:
Naval by Sherwin Williams: SW 6244
Hale Navy by Benjamin Moore: HC-154
Gravel Gray by Benjamin Moore: 2127-30
Newburyport Blue by Benjamin Moore: HC-155
Polo Blue by Benjamin Moore: 2062-10
Midnight Navy by Benjamin Moore: 2067-10