Rabbi Yehuda asks; why the markings of the doors of the Israelites were done with blood? And he explains that the blood they used came from two sources. The first source was from the ram they were ordered to bring home and slaughter after four days (Exodus 12:6,7). The second source is the blood of the circumcision. They mixed the blood and marked the doors in three sides for the three lines of the Tree of Life. Even though the color of the blood is red, the blood of the circumcision has the aspect of Right, Chessed, Mercy and the blood of the Ram has aspect of Left and judgment. The mix of the two created the balance of the central column, aspect of the green color.
Rabbi Yehuda adds that the Holy One Blessed be He transformed the blood to mercy that is white color as it revealed in the verse below when it says, “in your blood,’Live’”
“וָאֶעֱבֹר עָלַיִךְ וָאֶרְאֵךְ, מִתְבּוֹסֶסֶת בְּדָמָיִךְ; וָאֹמַר לָךְ בְּדָמַיִךְ חֲיִי, וָאֹמַר לָךְ בְּדָמַיִךְ חֲיִי.”
““And when I passed by you and saw you wallowing in your blood, I said to you in your blood, ‘Live!’ I said to you in your blood, ‘Live!’”
This explanation tells us that there was no dependency on the color and instead it was the markings on the three sides, right, left and middle.
Rabbi Chyzkiah reveals that the sefirot of Chessed and Gevurah that represent the two bloods of circumcision and of the Ram were seen at that time. The center line that is Tiferent included the two sides that are mercy and judgment.
The circumcision has the aspect of Mercy because it was given to us as a precept to correct the first sin. Removing the foreskin that is a Klipa over Yessod helps us control our desires and achieve greater purity of the vessel. The blood of the circumcision comes from a living child and that is why the verse above says “In your blood, Live!”
The blood of the Ram is judgment because it was killed for the aspect of disconnecting from the control of idol worship that was strong in Egypt.
Rabbi Ashlag mentions that the white and red aspects are like the sun that have white and red and together it gives the sun the color ‘green’ that is center column, Zeir Anpin. The Sun has aspect of mercy when it brings energy to support life in this world. The judgment aspect of the sun reveals when it ‘burns’ without restriction.