None. The W3C/CSS named-color set has no entries beginning with Q — one of several letters (along with E, J, U, X and Z) with no CSS color keyword.

Queen Blue is a medium, slightly dusky tone of royal blue. It was first recorded as a color name in English in 1926; before that, since 1661, the same color was called “queen’s blue.”

It is a synthetic organic pigment (quinacridone, PR122) widely used by painters and printers for its bright, lightfast purplish magenta. It is the same pigment family that gives process magenta its punch.

Q is a rare initial letter in English, so few color names begin with it. Most cataloged Q colors — Quartz, Queen Blue, Queen Pink, Quick Silver, Quinacridone Magenta and Quincy — appear on Wikipedia’s list of colors.