Paradise Lost

I'm currently reading the Norton Critical Edition of Milton's Paradise Lost. It's a worthy edition of the text that includes outside sources, explanations, and any further reading that the good ol' boys at Norton feel are relevant. So, there I was nestled into Book One, during Satan's heroic speech upon being booted from Heaven, when I noticed the word colour spelt, "color". Now, call me a square, but why have the Americans felt the need to alter the text in this albeit minor, and arguably, insignificant way. Yes, if it is insignificant why would I be frustrated by it? In the same vein, however, if it is so insignificant, why the need to change it? They have not replaced the word "yon" with your, nor the word "hath" with has, which would both modify the text to an extent to bring it into the modern American world. I'm sure the literary elite of America who come to read Paradise Lost will be able to skirt the syntactical differences that, I'm fairly certain, had not been altered from the original English for some 200-odd years. Considering the great efforts they've apparently taken to make the text as recognisable to Milton's vision as possible (excuse the pun), why leave out the u? Typical.