It's actually the worst color out there for this, either because of the way our eyes work or because there are so many colors labeled "blue" that look like hell next to each other.

I think the shingles will read more grey than blue and there's enough variation among them to allow you a great deal of latitude in the color you end up with for the shutters.

Been reading up on this and am not looking forward to my own paint adventure this fall.

http://www.thecreativityexchange.com/2013/06/tips-and-tricks-for-choosing-exterior-trim-colors-color-palette-monday.html

Just kinda thinking off the top of my head here.

1) Take a pic of your roof, then print it. Go outside and hold it up, looking at the roof and the pic. Adjust colors on the pic and print again till you have a good match.

2) Most all paint stores have a scanner type of device to match colors. Have them scan your pic to get a match.

or get a swatch from the shingle manufacturer.

could be a lot more shift between camera and printer and paint matcher than you might think.

I think you will get more advice. Like I'm thinking a different color for the house. The blue roof probably makes less difference than the contrast between the house color, the trim, and the shutters and door colors.

and the blue I picked looks like "recycle bin blue". I used a color swatch to be what I *thought* would match the shed that my Dad built and that color is Behr's "Biloxi", but after looking at it in regular light, (I picked it in grief throes) I was horrified. LOL