Thanks for your replies. You make good points.
I don't think I will worry about the ratings.

You're right. Chess is unbalanced too since
someone moves first. However, the amount the
game is unbalanced is very slight (and while
a big factor with grandmasters, it is virtually
unnoticeable by amateurs), and I conjecture
that it is much more imbalanced in a game like
horde chess. For example, a friend of mine and
I played horde chess. I played five with White
and he played five with White. It ended
up that one particular color (not one
particular person) won all ten games.

So, I would distinguish between those unbalanced
games where the lack of balance comes from
granting someone the first move and where the
lack of balance comes from an asymmetry in the
starting position (especially huge asymmetries
like in horde chess).

On the other hand, first move alone *can* be
a big factor in some games, even to amateurs.
Go-Moku springs to mind. I haven't completed
any atomic chess games, but I suspect that first
move in that game can be a huge advantage too
(I may be biased because I am currently losing
an atomic chess game with black and it's only
the 4th move!).

In any case, getting separate color ratings for
asymmetrical starting positions at least makes
a lot of sense to me.

Just a thought. I don't feel passionately about
it or anything. I probably won't play such
games here anyway.

I noticed that some of the games, like horde
chess and Maharajah chess, have asymmetrical
starting positions. While a lot of thought has
probably gone into making these games "fair,"
i.e. equal chances for both sides, it is almost
a mathematical certainty that these games aren't
exactly fair. However, they are still fun to
play. I think that having separate ratings for
Black and White would be a good idea, since,
for example, someone who plays white 75% of the
time in horde chess would not have a rating
compatible with someone who plays white 25% of the
time in horde chess.