The majority opinion is that, when we had the tradition on techeilet (the wool-dyed-blue string on tzitzis), each corner of the garment would have 7 white strings and one techeilet string.
If I've heard correctly, Rambam has the interesting opinion that the 7 strings should match the color of the garment. Red tallis means 7 red strings and 1 techeilet string. (We don't follow the Rambam!)
But according to Rambam:
- If the garment was entirely techeilet, would it get 8 strings of techeilet?
- What if the garment was entirely kala ilan (indigo, the Gemara says it appears close enough to techeilet to fool people; it's also chemically identical to some of the techeilet formulations out there today)? 7 strings of pseduo-techeilet and one of real techeilet?