People in this time period did not really care about skin color. Hatred was based almost completely on religion, ie Christian vs. Muslim. Like an above poster said, no Christian monarch would ever marry his daughter to an infidel Muslim, he would be very unpopular with his people, the Church, his other children etc.

Historically, if I am not mistaken, Richard the Lionheart wanted to marry his sister to Saladin's brother but she refused because of the religious differences and general hatred toward Saracens (again, due to their religion and the perception she had about them).

As far as the game is concerned, I know not if the programmers purposely made it more difficult for Muslim princes to marry Christian princeses, but like another poster said, The influence of your king makes all the difference. I had my Turkish Sultan get numerous marrigae offers after boosting his influence.

Also, I would add that Muslim princes had a lot of women to choose from and I don't think they used marriage as a political weapon like Europeans tended to do.

For those that care to read, there is my two cents.

Thank You.