One of the old lavenders
Lavender gray is a pale gray with a faint blue and purple cast. Maerz and Paul's A Dictionary of Color of 1930 treats it as one of three main kinds of lavender. The other two are lavender blue and floral lavender. The same book also lists old lavender, a darker gray version.
Where #C4C3D0 comes from
The code follows the ISCC-NBS color system, which calls this shade a light bluish gray. It appears in the Wikipedia article on lavender, which also points to a close Prismacolor pencil called Greyed Lavender. Compare it with old lavender and lavender blue. The CSS keyword lavender is much paler and has less gray in it.

