Another name for periwinkle
Lavender blue is another name for periwinkle, a pale blue with a touch of purple. Both names share the code #CCCCFF on this site. That code matches the periwinkle in Maerz and Paul's A Dictionary of Color of 1930.
The same book dates the name blue lavender to 1926. The Oxford English Dictionary records periwinkle as a color name from 1922, according to the Wikipedia article on periwinkle.
More color than web lavender
The CSS color lavender, #E6E6FA, is so pale it is almost white. Lavender blue keeps red and green at 204 and turns blue all the way up, so the blue shows clearly. It is still a light color. Black text on it reaches a contrast of about 13.7 to 1.

