Euphorbia 'White Ghost'

I'm a beginner- completely! I have recently purchased a Euphorbia Lactea and now a few weeks later it has developed these blackish patche...Read Mores on the parts where the variegation is the darker green color... :-(
My guess is the darker green colored area is where there is more water or fluid at the surface? Or perhaps because euphorbias are supposed to have a milky liquid, ...the darker green albeit sort of translucent part is the area where there is more clear liquid or air pockets? normally?
I have only watered it once, and minimally! I have researched around & don't find a description/image which matches....any advice? I can send/post a picture.

My e. lived as a houseplant for one year, by a very bright window with little water. It outgrew its indoor pot so I moved it outdoors in...Read More full TX sun. It never missed a bit, it never burned. It has gotten no winter protection in the last two years but I do cover it if we get more than a day's rain. Excessive moisture would kill it fast.

When I first got this plant, I was under the impression that whoever added it to the plant files knew a lot about it.. .but that was obvi...Read Moreously incorrect, as it is a much hardier plant than listed here (originally- hope to get that changed)... I have grown it outdoors in zone 9b under protection, but it is marginal there... however, in zone 10a it is perfectly adapted here in Southern California, even to full sun (which also was not listed above), though probably morning sun would be the most ideal situation. When I first got it, it was a greenhouse plant, and did burn in the sun a bit... but it has been growing in hot sun up until just past noon now for nearly 2 years without a hint of burn... and easily takes temps down into the low 30s (30 even, in fact). It is planted outdoors in the ground and took 4 months of cold rain this last winter without complaint, as well as the 120F day we had this summer (along with at least 40 other days of >100F ). It is a relatively slow grower, at least compared to the 'regular' form of E lactea, but still I have seen many specimens in greenhouses, and a few outdoors 10' tall or more. It is a beautiful and quite hardy species for the warmer zones and makes an incredible landscape plant.