true blue

Example: “She's a true blue friend; she drove four hours to help us move.”

Origin: Documented from the 1660s and 1670s, with two rival stories competing to explain it. One points to Coventry, England, whose dyers were famous in the late medieval period for producing blue-dyed cloth that held its color reliably through repeated washing, rather than fading — a reputation solid enough that John Ray's 1670 proverb collection already records "true blue" as a byword for someone dependably, unchangeably themselves. A second theory reaches for 17th-century Scottish politics: the Covenanters, defenders of Presbyterianism against the crown, adopted blue as their movement's color specifically to distinguish themselves from royal red, with "true blue Presbyterians" documented from 1663 as a term for genuinely committed, steadfast supporters of the cause. Neither theory is clearly established over the other, but both converge on the same underlying meaning: blue, whether from a dye that won't fade or a political loyalty that won't waver, as a color standing specifically for constancy.