Question about lavendar.

Which lavendar is the darker/darkest blue, everything I 've got seems fairly light. Does being in the bright sun make it darker?

Colour is one of those things you can't guarantee. It sometimes has to do with the soil and local climate but most of all it's the beholder :)

If you want the darkest Lavenders then look to the Lavandula angustifolia cultivars (Common Lavender or I suppose you might call them English Lavender).

Hidcote is considered the darkest
http://montereybaynsy.com/L/lavandula%20angustifolia%20hidcote2.jpg

Loddon Blue and Royal Velvet are also very dark for Lavenders, the link picture is of Royal Velvet
http://www.goodwincreekgardens.com/Images/Products/royvelfull.JPG

This is a link to Norfolk Lavender where they have 3 pages with various cultivars of several species and hybrids listed.
http://www.norfolk-lavender.co.uk/catalogue/show-plants2.cfm?pid=1&s=1&mall=0&store=0&cat=0&textonly=0&

Thanks,Baa, that Royal Velvet looks like such a bright clear blue, and the Hidcote looks quite dark, I suppose as they dry they lighten? Have you ever seen what we call Loddon Blue Anchusa? The Royal Velvet color reminds me of the blue of this anchusa. I have had this anchusa twice but have not been able to winter it over even being a perenniel.

Lavender flowers will certainly lighten with drying.

The Anchusa sounds like Loddon Royalist which is the name here. It's a beautiful blue but it's not one I've personally grown. Anchusa azurea have a reputation here for being short lived.