Inspired, I came up with this:
This is not a pattern, but a guide to making your own pattern.
To figure out how many stitches to cast on:
Make a swatch and figuer out how many stitches you knit per inch. Measure you wrist, add 1/2 inch for movement. Multiply the measurement, in inches, with the amount of stitches per inch you get from your swatch.
Example: My wrist is 7 inches + 1/2 inch for movement = 7 ½ inches. My swatch gives me a guage of 8 stitches per inch. 7,5 times 8 = 60
I casted on 60 stitches and used 2 mm double pointed needles and 2-ply scrap wool yarn.
The ribbing is a knit2 purl2 rib, using the background color for the knits and a mix of the other colors as the purls. I ribbed 8 rows.
The first pattern is a simple zigzag, this pattern repeats 3 times on the mittens, I put it first, last and in between the larger patterns.
The bigger patterns are from the book, but there are so many nice free Fair Isle patterns to copy. Search pattern databases such as Ravelry (this requires a log in id, but it's free) and Drops (write "fair isle" in the search box). I added a couple stitches to accomodate the patterns.
The pattern in blue is a OXO pattern. I used the X to give me a starting place for the thumb increases. I added first one stitch in the middle of the X and then one stitch on each side of the first increase every other row for a total of 14 extra stitches. The other pattern continues on both sides of the thumb increase.
I kept trying the mitten on my own hand, figuring out how many stitches were needed and how long to knit before putting the thumb stitches on a thread.
On the next row, I just skipped the thumb stitches and joined the remaining stitches together, continuing the knitting until I got the length I wanted.
Row 1 (that is row 1 of the edge, it's probably your row 145 or something ): ( k2tog, yo ) repeat until end of the row.
Row 2: knit all stitches.
Row 3-7 knit all stitches.
Cast off loosely.
Turn the edge at the k2tog, yo row and sew the hem to the back
Pick upp the stitches on the thread and pick up as many stitches as you need from the back of the thumb. I picked up 6 stitches. Knit as far as you want. Cast off.