Mmm. Looks lovely. The stripes in the photo - looks like they worked the light-colored stripe for twice the number of rows that the other colors were worked. i.e., if you do 16 rows for most of your colors, the lightest color would be worked for 32 rows.
I believe in tying knots when introducing a new color. If you've ever worn stockings, you know how easily knitting unravels. Why create a weakness [untied new yarn] when you don't have to? Please note that others have a different take on this.
Your knots/new yarn would be at the edge.
Good luck! Lacy projects are a mark of a top-grade knitter.