Not quite accurate. There are currently 2 McDonald's in TLV, one pre-security, and one post-security. They are owned and operated by the same people. They applied for a Teudat Kashrut from the Rabbanut (I think of Tel Aviv-Yaffo,) and were initially rejected. The Rabbanut said that in order to get the Teudah, all McDonald's throughout the country would have to become Kosher. This was challenged in court, and overturned by the High Court of Justice. So now, both operate with a Teudah.
Last year, a similar thing happened when McDonald's opened in Tachana Merkazit in Jerusalem. Many Jerusalem residents petitioned the Iriyah to ban them from opening unless they become Kosher. Once again, the Rabbanut wanted all McDonald's to become Kosher, including the one off Ben Yehuda and the one on Emek which are both not kosher. In the end, a compromise was reached, in which the one in Tachana Merkazit is blue instead of red. None of these 3, nor the Kosher one in the Mevaseret Tzion Mall, are open on Shabbat.

So, how many blue Mc Donalds can be found throughout Israel?

Just the one