You're banishing Earth only, but the color is bright blue, and you're intoning Adonai in the South Quarter.
This is a common misconception, you are not banishing Earth only, but rather using the same form of pentagram as Earth to banish everything. Another way of looking at it is that Earth is the summation of Fire, Water, and Air according to some Hermetic and Qabalistic texts.
I believe electric blue is a modern addition, pure white light will serve just as fine if you feel it more appropriate.
As for Adonai in the southern quarter, the God names do not refer to elemental quarters, but are pure expressions of consciousness. You could read them like this
"YHVH (The Universe/all of creation), Lord, I am that I am, Thou art Forever and ever Lord." It is a form of prayer, as well as stating the inherent divinity within and aligning consciousness with That.
You may find Crowley's comments on the ritual useful, these can be found here:
http://hermetic.com/sabazius/ac5nts.htm93s
"Anybody who has been seriously engaged in scientific work of any kind realises that over the entrance to the gates of the temple of science are written the words: 'Ye must have faith.'"
-Max Planck