I've had some blue collar ones all the way up to software engineers and everything in between. 

Look for areas with solid rental demand, typically in Blue Collar America, where BTR projects are particularly appealing.

I go a little more blue collar outside of the city and can get 20% 

I love the blue print they made for me showing how all my businesses, trusts... are laid out.

With a mix of college students, medical professionals, and blue-collar workers, the rental market stays pretty steady.

Blue skies always! 

That is more likely to happen with a blue-collar, middle-class worker than it is with a wealthy person.

I left with a sniffle, with bleeding fingers, cracked lips, and a perpetual risk of a nosebleed in the heart of Denver winters that get so cold, my toes start to turn blue after 5 minutes outside. 

I personally know several blue-collar millionaires from HVAC techs to plumbers.

Check out this thread on Norada Capital Management here on Bigger Pockets where out of the blue this big syndication suspended payments to all it's (many) members:https://www.biggerpockets.com/forums/960/topics/1196567-nora...