Lavender Colours

I'm looking for a lavender cultivar with blooms that come close to black. Another web site made passing reference to Wings of Night lavender. Do you have any information on this one? Would it be hardy in zone 6 dry heat of the Salt Lake valley? If not, is there an alternative black?

We are not familiar with the 'Wings of Night' cultivar. If it is a variety of Lavandula angustifolia, or of L. x intermedia (hybrid between L. angustifolia and L. latifolia) it should do well in your conditions. You may have to water during droughts, because lavenders are Mediterranean plants and do best if they never dry out completely, yet have excellent drainage. If this cultivar belongs to another species such as Lavandula dentata, L. multifida, L. pinnata, L. stoechas and L. viridis it will not be winter hardy in zone 6.
We are sorry, but we don't carry any lavenders that are close to black in colour. Probably the darkest variety we carry is 'Twickle Purple' which has a deep purple flower. It is hardy to zone 6.

What cultivars would you recommend as the closest to true royal and sky blue?

'Hidcote' and 'Twickle Purple' are probably the closest to royal purple, and 'Munstead' lavender closest to sky blue.
It is very difficult to match colours precisely, especially when grown from seeds because there is a natural range of variation in seed grown lavenders both in growth characteristics and in flower colour.