Mendy Hirth asked:
What if the strings are green or red is it meakeiv?Do you need a shiur of white?What if it was inserted white & became discolored later?
The Kollel replies:
See the Gemara on 40a, where the Gemara says clearly that Tzitzis colored blue, but not Techeles, are Kosher for Lavan. See Rambam in Hilchos Tzitzis 1:1, who says that the white Tzitzis are called white for we are not required to color them. However, see Tosefos 38b (DH Midi) who proves from the Gemara on 41b that the Lavan must be the same color of the Talis and his conclusion is that it may be a requirement d'Rabanan. (See also Insights to Menachos 41:2.)
D. Zupnik