I have seen many pictures of people from Iran, some of them have been white, a bit of them have been reddish or light brown similar to Arabs, Berbers, or other Bedouin, but most of them have been of a fine swarthy complexion. If you look at these pictures and look at Cyrus yes, it may appear that he is a bit too light.
However, what many people fell to realize as they talk about skin color (this guy is so light/dark, the X people are a shade lighter/darker whatever), is that skin color CHANGES depending on how much sunlight someone gets.
For example, look at this picture of a Arabic Bedouin,
http://www.jordanjubilee.com/images/bedouin/Cheikh_Attaieq_5_90.jpg
Our chap looks like a pretty stereotypical Arab dark skinned Bedouin, not black but a nice shade of brown. Lets say that this guy has a son. At birth this Bedouins child would be probably of a lighter complexion, if he stays in the sun like his papa his skin will darken and become the same shade as his father. If he doesnt hell probably stay light skinned. Hell probably look more like King Abdullah of Saudia Arabia.
http://en.wikipedia.org/wiki/Image:Abdullah_of_Saudi_Arabia.jpg
Both of these guys are Arabs. This is also why all through out the middle east bedoins seem to have a darker skin then city dwellers, they aren't exactly a different race usually, they just get more sun.
Usually the elites in the upper classes of Middle Eastern society were light-skinned, they were more or less the same race of the populace; they just didnt do as much backbreaking work in the sun and thus stayed light skinned as they where at birth. This is also the reason that usually lighter-skinned women are sought after practical the world over. This proofs that they arent of common birth and had to work in the fields. (Even in Africa amongst the black Yoruba, I once read that they seek after light skinned women, mind you not white, yellow or red women but women who has kept her dark brown complexion from her birth.)
Getting slightly back on topic, bearing in mind that Cyrus comes from high class and is a King. It would be highly unlikely that he would have a very dark complexion. Saying all this, I do agree he should probably a TAD bit swarthier and have a black beard (even though I have seen light haired Irans they have been in the minority by far).
@Morgrad believe it or not, many people from central Asia can have dark or swarthy complexions by staying in the sun, you could say that they tan easier then most Europeans. Not all Caucasians are Nordic white!
At the very least, this is the way I see it. Take it all with a heap of salt and eggs in the morn.
PS when I say dark I am not referring to black. Theres more to skin color then just black and white tones.