Quotation for Berakhot 18:35

From when does one bless on the ציצית [that he puts on] in the morning? From the time when [there's enough light that] one can tell the difference between the techeilet (blue) in it and the white in it. And if he puts it on starting at dawn, some say he makes a blessing, and this is our practice (Mordechi - chapter 2 of Tractate Megillah). And if he put it on earlier than that, such as during [the time of year when we recite] selichot, he should not make a blessing over it [right away], and [then] when it becomes light he should touch [the ציצית] and makes the blessing (Tashbe"tz).