The performance of KBG is not that soil dependent, but with sandy soil you have to realize your soil won't hold nutrients as well as soils with more silt or clay, so you might fertilize more often, but with less fertilizer (splitting apps). A good soil test will reveal your CEC which will help you determine if this is necessary. Watering schedules might have to be altered as well if your soil has very fast drainage. I could write a lot about the darkest cultivars, but I will refer you to the current NTEP trials for KBG (www.ntep.org). It is recommended that you use a blend of three or more KBG from different subgroups (the convention is one from the compact, compact midnight, and compact America but you can add others if you want). Most of the compact midnights are similar in color and they are all dark as they have highly conserved genes. Bewitched and Prosperity are two very dark cultivars from the other groups I mentioned, but there are other ones that people use that have dark green color.

To emphasis tiemco's advie: By all means, use a blend of as many cultivars as posible (bare min is 3) to help avoid diseases that can decimate a lawn of a single cultivar.

I have to disagree with with you grass1950, using three is sufficient enough and is in line with recommendations from most turfgrass programs. The newest KBG cultivars have very good disease resistance, so good that there are some who think planting only one good cultivar isn't such a bad idea (see link).

http://buckeyeturf.osu.edu/index.php?option=com_content&view=article&id=1067:kentucky-bluegrass-cultivars&catid=1:latest-news&Itemid=170

You are always welcome to disagree tiemco. Without the opportunity to disagree there wouldn't be any sharing of ideas. However that is a short article that has to be at least 2 years ago ( I'm a buckeye--so osu is god in Ohio), as I read it when I was preparing to renovate in 2010. In fact, it was the major reason I was going to use midnite only. But I got cold feet and added the other three cultivars. enuff bout me--blah, blah.
I agree most programs recommend 3 cultivars and the more cultivars, the more attention that must be made to compatibility between them, color, growth rates, etc. per NTEP. The article states that an article by Dr. Brede "suggests" that one cultivar "might" be a valid paractice. The problem I had was I couldn't find any follow up reports or studies that supported their supposition. (something may have come out since--if you are so informed please post the addy for me as I am interested) In fact I couldn't even find Dr. Brede's article (bad searching maybe). It's just that at almost $4 a pound for good improved cultivars and all the work involved, I wasn't willing to take the gamble. On that basis I don't recommend it, or planting less than 3 different closly compatible cultivars slthough anything more than 5 or 6 is overkill and very well might lead to its own problems (too little of one cultivar to have an opportunity to germinate, grow and blend in.) I 'm not going to to draw a line in the sand about 3 vs more. 3 is still sound advice.

"To emphasis tiemco's advie: By all means, use a blend of as many cultivars as posible (bare min is 3) to help avoid diseases that can decimate a lawn of a single cultivar."

The above is your original post. Your advice to use as many cultivars as possible is misleading (so 10 would be great right?), and by saying 3 is the bare minimum isn't correct and it makes it sound like one should use more. I don't advocate growing a monostand, but my point was that today's KBG is much more disease tolerant than it used to be, and 3 cultivars is more than sufficient.

The conclusion of that study was that of 98 plots, mostly blends of 2-6 cultivars Award performed better than all but nine of them.

Yes, I guess I could have written with more specificity in my first post. But three (3) is still the recommendation of every turf program that has made a recomendation regarding KBG that I have ever seen. If three is what all programs recommend, One can safely state that a bl;end of 3 is the bare minimum. If you use well matched cultivars there is certainly no harm in using a blend of more than three (3) and there are advantages (yes it may be belt and suspender-- but there is no harm, no extra cost, and more insurance against a lawn destroying disease or pest)
Of course, tiemco, it must have been your intent to give people the impression that the planting of one cultivar "might" work, so I hope you are willing to take their wrath if it doesn't...Although I understood your point, per your logic, some may have misunderstood...I didn't see any disclaimer to: "The newest KBG cultivars have very good disease resistance, so good that there are some who think planting only one good cultivar isn't such a bad idea."
What seed supplier do you know that bags more than a 6 cultivar blend? The suppliers/resellers I'm familiar with have single cultivar and 3, 4, 5, and 6 cultivar blends available. I'm sure a seed supplier would explain that a request for a special blend of 10 different cultivars is misguided.
You are knowledgeable and I respect that, but you are not infallible and frankly, you can be quite disagreeable and at times demeaning to people.
Your sarcasm is not appreciated. (Ahem, it is not like I implied that there are "liquid aerators." -- a completely misleading statement.)
That's the end of this "disagreement" as far as I'm concerned.