If the question is the percentage of blue-collar whites who are Democratic, then that doesn't require that most people overall, or most Democrats, be blue-collar white Democrats.
Blue-collar whites in most northern cities (here as opposed to suburbs) are a Democratic constituency. I believe from earlier precinct discussions on this forum that none of Seattle, Portland, Minneapolis or St. Paul has a Republican precinct that isn't a religious college or a very rich area, and yet there are definitely parts of these cities that are substantially white and blue-collar. Further east it gets a bit complicated with the history of white flight backlash, but there are still strongly Democratic working-class areas in places like the west side of Cleveland, much of Pittsburgh, etc.
My hunch would be that in some of these urban neighborhoods the D vote among blue-collar whites is higher than in any more rural area that stands out more on a map, but this is hard to prove. And of course "blue-collar white" is kind of a vague category.
Lower-income Portland neighborhoods without a significant urban professional or young adult contingent are strongly Democratic. Depending on the location, working class Portland neighborhoods regularly give Democratic candidates between 55% to 80% of the vote. Unfortunately, determining the percentage blue collar whites give to Democrats is tough in many of these neighborhoods because as gentrification proceeds, immigrants are relegated here and this is rapidly changing the character of East Portland.
In general in the NW, there is a pretty strong correlation between the white working class and prevalence of lower income Asian/Latino immigrants and even African-Americans to an extent that makes a determination of blue collar, white voting difficult.
Off the top of my head, here are some urban areas containing significant contingents of blue collar, white Democrats:
Tacoma
Spokane
Flint
Toledo
Youngstown
Allentown