You're confused, yes, but understandably so. I'll try and explain:
With the exception of the early containment procedures, this article is written from the point of view of researchers who have already been 'infected', or who have realized they soon will be. The photo spreading the infection is a moot point, and I mostly put it in as an out of character way to clarify the effect. Assume that the photo was one someone found after the SCP was given the -EX designation and that they attached it for similar reasons.
As to the unclear effect… well, your mileage may vary. I've had some people get it immediately, and a few who have PM'd me and still don't understand. I ran into the problem of describing color from the perspective of characters who already had the concept of color, but a different definition entirely. They had a "blue", but it wasn't what we now see as blue; I couldn't write "everything went from black and white to color" because in-universe that's not what happened.
You see, the science of optometry still has yet to prove or disprove whether the shade one human being perceives as "red" actually looks anything like another person's perception of the same visual wavelength. It's totally possible that everyone's brain actually interprets the visual spectra in wildly different fashions, and there's no way at all to test it, really. (For a great example of this, try asking a color blind person to explain what they see green or red as, and prepare to be baffled.) As a result of this confusion, there are no really tangible adjectives for describing color.
The point is, it's difficult to describe a color without resorting to "well, it's… uh… reddish?", which for my purposes wouldn't have worked at all. I realize it's a tad hard to catch at first, and I'm open to suggestions, but I think it's about as clear as it can be, seen?
The last bit is a stylistic choice, really. I like to put containment addenda in the containment section for clarity, but it's basically up to the author.