http://deskthority.net/wiki/Dell_AT101Black Alps on all the Windows key versions. Pink Alps on many of the previous versions. A few domes. The SGI Granite version (basically the same board) used damped cream Alps.
Not aware any ever came with blues – at AT101 family is all tactile switches.
And yes, blue Alps are both really smooth
and really tactile as well. Unfortunately, the Alps heyday ended before Windows-key-based keyboards came into being, and the AT10*W boards are amongst the very few Alps CM boards with Windows keys or the standard Model M layout (though I read that the Model M copied a previous keyboard's layout). Decent Alps basically means nutter layouts.
Even then, the AT10*W keyboards have inferior scrapy switches. It's debatable whether the older tactile switches (e.g. pink) were better or not – I briefly tried a vintage Apple board with what would be either pink or orange and that was really smooth, or so it seemed at the time. Should have bought it, then I'd have a comparison. Maybe Alps switches just wear smoother with use? My AT102W was NIB, after all and it sees very little use, just a spare board at work on the test/setup bench.
I am looking forwards to the Matias Quiet Pro when it ships to Europe next year (already pre-ordered). I want a nice quiet but tactile switch for work, but it will also tell me how nice a Matias switch would be if it was sold undamped, as tactile Alps switches have a great sound. My AT102W sounds a lot nicer than my MX brown Filco or my G80-3000 with clears.