White collar architects are artists, and spend their time designing. Then they hand their sketches to structural engineers and say "Figure out how to build this." These are generally the folks architecture magazines write about.
Blue collar architects are more engineers and tradespeople, and see success as a building that fits the purposes of the client, in budget, in a pleasing way. They're more likely to repurpose a historical form, if it's well suited for the request at hand.
One of the central features of architecture meta is that white collars think blue collars lack creativity and intelligence, and blue collars think white collars are pompous pricks.