Jayme Hobbs Take a pic of it to the paint store/pick out multiple sample swatches. Take them home and compare in your lighting to each other, and the room. And/or ask a paint expert to match it...but in my experience taking a swatch home and putting those in the room u want to paint/watching how it looks at night vs. day, vs light on and off...works well. I got our bedroom perfect doing this. It also was a blue/but more of a robin's egg blue:)
http://www.houzz.com/discussions/276597/Need-help-with-paint-colors