2/22-2/23: My hands are larger (20 cm circumference at knuckles & 14 cm from top of thumb join to longest finger tip) so making some modifications to fingering weight pattern:
Added 8 stitches to cast on
Did ribbed cuff for 2 cm
Did cuff for total of 9 cm before starting hand shaping on the first full black stripe row.
Decrease rows (16) on my mitten should take 3.25 cm so will work 10 cm from where I removed thumb stitches or 3.5 cm from fingertip (first full blue row).
Did one extra set of decrease rows.
I needed a few extra inches for the Kitchener but I like it. It took me one weekend to finish one mitten (no thumb)

2/28-3/1: Working on second mitten and it is a pretty close match. There is only about 10 cm difference in yarn when I cast on so the second one has half a row more of the red. Time to do the thumbs!

3/1-3/2: I did the thumb on one hand exactly to the directions but it was too tight in circumference. On the second mitten I picked up 3 stitches in the gap instead of 2 and did not knit them together with the stitch on the needle. This circumference is much better. I knit the length of the thumbs until it was just at the tip of my thumb and then did the 2 decrease rows.

Thumb Note: The first thumb I started with the blue yarn section so the stripes would be continuous but this made the entire thumb blue since the circumference wasn’t as large as the hand. It looks ok but I wanted to experiment. On the second thumb I started the thumb at half way through the blue yarn, this means I got a blue, black and a row or two of the red. The stripes aren’t the same thickness as the mitten, which doesn’t bother me, but is in the same spirit as the mitten. I have to rip out the too small thumb on mitten 1 anyway so I will repeat that method so my thumbs are multiple colors. Another thing I would like to try on my next pair is to take off the thumb stitches at the end of a color sequence. This would have allowed me to have any color thumb I want without one row of stitches in the blue color. A red and a blue thumb may be fun and allow me not to waste so much yarn.