True blue will never stain.
This proverb means that someone who is loyal and trustworthy will always remain so, even in difficult situations.
“True blue will never stain,” appeared in James Howell’s proverb collection of 1659. It referred to a blue dye that never ran, and therefore the color came to symbolize constancy, or, as John Ray described it in 1670, “one that was always the same and like himself,” a man of fixed principles. In Britain it was applied to loyal members of various groups, the Presbyterians of Scotland, the Whig Party, and later the Tories (whose official color was blue) and various university varsity teams. In America in the 1900s the term referred to team loyalty but has largely died out.
True blue
Loyal, faithful, as in You can count on her support; she's true blue. This expression alludes to the idea of blue being the color of constancy, but the exact allusion is disputed. One theory holds it alludes to the unchanging blue sky, another to the fastness of a blue dye that will not run. Blue has been the identifying color of various factions in history. In the mid-1600s the Scottish Covenanters, who pledged to uphold Presbyterianism, were called true blue (as opposed to red, the color of the royalists). In the 1800s the same term came to mean "staunchly Tory," and in America, "politically sound."
