Blue collar is a slur used to describe Mexicans in a derogatory way. Many illegal immigrants take manual labor jobs.
The word Blue collar is a racial slur that has been used historically to degrade and dehumanize mexicans. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to mexicans. If you are unsure about whether or not it is appropriate to use the word Blue collar, it is best to err on the side of caution and avoid using it in any situation.