Make the bits struct more complicated. Also, since it's sufficiently
non-trivial, make the various color representation changing function
mutate the representation to represent the change that was being made.
(And give them better names)

Also, I needed to update the test cases to make `feq` not fail on the
large values (65535), since that + the epsilon of 1e-6 exceeded the
floating point precision. And apparently we never actually linked the
test cases against libm etc.