next time you get a chance,... examine one of the master's kite building effort up close & personal,.. see how Ron Gibian does it? What is his seam width,.. how many stitches per inch, .... do you want "black" on both the front and the back sides, like him?
The Randy Tom method (sew all the fabric colors together for the entire sail, then front and back cut out the appliqué pieces until you're left with just a single thickness). Wastes huge amount of fabric, but nothing can slip/slide/or wiggle out of alignment, there are no hot tacking holes either, no gummed-up sewing machine, your efforts are expensive but completely perfect, like your own national entry into the AKA building comps?
Some folks (Lam Hoac) "mount" all the colors onto a white carrier piece of fabric, easy to see the lines, simple to butt the pieces and an accurate fit of the appliqué based upon experience. Now you have to hold those pieces in position as you slide thru the sewing machine. What is your solution?, masking tape, hot tacker, spray-mount adhesive, water adhesion thru a capillary action? You do NOT back-cut out the backing layer, the white stays one piece. Ask Lam for a black kite and oh how he howls, back-cut out the backing layer yourself and now he's concerned if you did a good job,... "cause his name is on it!"
Did you know you can make the entire kite with no sewing at all? 3M's 9460 VHB adhesive tape,... I've flown single skinned quads of this construction method for 3,000 hours. Guess what?, no weight of the thread, no excess overlapped seams, no perforations (sewing needle holes) to promote early failures. It is not faster, just another choice to be made as a builder.
Here's a word to explore,... if a dualie sport kite is your interest: catenary cut,.... that's where you adhere a curved surface to a straight edge, thereby making a 3 dimensional shape w/o any framing to force that shape. Like a tent instead of a tarp. Who's the master of this technique?, Ken McNeill, blue moon kites. Until you have personally experienced a kite built this way, ...... anyway, more options to consider as a builder.
If I wasn't so impatient I'd be making my own kites too, alas I know my own serious flaws and deal with 'em, accordingly. I will pay for expert production by a true master class builder who signs their work and backs the product.