This is variation on a traditional pattern mostly used in the Hardanger region of Norway.

The most common colorways are : natural white and natural black ( charcoal). Other varieties used in Norwegian traditional mitten knitting is : red and white or red and black.
Substitute the green in the pattern for the white if you want to do a more traditional version.

The ribbed knitting is usually done in the pattern color (green).

The intarsia pattern is a repeat of 8x8 stitches.

I recommend knitting a small sample to determine if you need to scale up or down. If you want to alter the size :
Scale down : use a smaller size needles or reduce the pattern with a repeat (8 st) or more.
Scale up : use larger a larger size needles or add a repeat of the pattern (8 st).

Shorten or lengthen the mitten by adding or removing repeats (8 st) from the intarsia pattern.

Make sure the thumb pattern matches any alterations.