Bob,
I cannot say what/when the DOW has stocked into Blue Mesa over the years, but I would doubt that true Loch Leven(Scottish) or von Behr (aka German Browns) would be present. When the various strains of brown trout were stocked into the US starting in the late 1800's there could have been some dinstinction. But their genetic lines have become so muddied over the years that anything in the US today is a "mutt" brown anymore.
That being said however, the browns you are catching could be exhibiting a phenotypic or visiual characteristic of Loch Leven browns that is still expressed. Silvery color is a recognized trait of Loch Leven browns, but this characteristic could also be caused by other dietary factors (i.e. eating too many hatchery reared rainbows). Another characteristic that is exhibited by Loch Leven fish is a blueish dot about 5 mm (1/4") above the eye. I have never noticed this in any browns I have caught in CO.
If you are interested in this subject there is book by James Prosek "Fly Fishing the 41st." This is the only book of his I have enjoyed, but it is kind of a cool account of his travels around the world following the 41st parallel North fishing for trout, with some emphasis on Browns and their geographic historic range from Europe to the Stans in Central Asia. I have travelled and fished in many of the areas in this book so maybe that is why it kept my ineterest.
I hope this helps.