This reverts commit 33da9b2327 and the
following commit dc08c48f33.
C++17 changed the behavior of static class member variables that are
constexpr defined. Previously this definition/declaration split was
valid for constexpr members, but after C++17 the static constexpr member
variables are automatically inlined, so the declaration is no longer
exported in some compilers (GCC 9/10/11 seem to have problems).
An alternate way of constexpr member variables is putting the
initialization in the class definition, but we can't init a COLOR4D
object when defining the COLOR4D class.
For now, revert this change until we can figure out the proper way of
architecting these colors.
18ea3be3f2