In the 15th chapter of Numbers, God commands Israel to wear ‘fringes’ on the corners of the garment which will include a blue thread. Now, Messianic Jews use the blue thread as a reminder that the Messiah (Yeshua) stood out among men as God’s son and we all ought to be mindful of Him. It is referred to as a Shamash. The blue thread is the only color that God speaks of that is to be in the tzit tzit. Some will argue that any other color is against God’s command; however there is no scripture stating that the tzit tzit are to be of a specific color, only to include the blue thread and they are to be worn every day..
They are usually attached to an undershirt of sorts referred to as a tallit katan which is worn under the shirt. There is also no scripture that says women are not allowed to wear them. Messianic Jewish women sometimes wear them whereas you rarely if ever see Orthodox women wear them. There is a prayer said before attaching them or before donning the tallit katan that goes like this; ‘Bahruch ahta Yahweh, Ehlohaynu mehlech haolam Asher kidshanu bemitzvotav vetzivanu al mitzvat tzitzit.’ Or when translated to English, ‘Blessed are you Yahweh Elohim, King of the Universe, who has sanctified us with His commandments, and commanded us regarding the commandment of tzitzit.’
There is a consideration some have in the Messianic movement that in the verse of Revelation 19:16 ‘And he has on his garment over his thigh the name written: “The King of Kings and The Lord of Power.’ Messiah will come back with His tzitzit on and the knots will spell out YHWH rather than the popular belief that the ‘name’ will be tattooed on His thigh. Tattooing is forbidden in God’s law therefore Yeshua (Jesus) would not violate His Father’s law. ‘The numerical value put on tzitzit coupled with the strings and knots usually equal the number 613, which is the number of God’s laws.’ *http://www.hir.org/a_weekly_gallery/6.11.04-weekly.html*