Use any number of colours, in any sequence you like - why not use up all those bits of aran yarn leftover from other projects?
The mittens are very warm and the stitch pattern is easy to do: the colour effect and texture are achieved solely by the use of slipped stitches, and knit and purl - definitely no stranded colour knitting necessary.
The mittens are knitted in the round. For the shaping, you will need to be familiar with the decreases k2tog, p2tog, ssk and ssp, and with the technique of grafting for the last few stitches. For size L a few stitches will be increased too, by making a stitch (or any other method you like to use).
The pattern has 3 sizes: Women's XS/S, M and L, with an inner circumference of the mitten of 18, 20 and 22cm (7⅛, 7⅞ and 8⅝”). Due to the peasant thumb, choose the size generously, so that it will also fit on the wider part underneath the thumb. Add 1-2cm to your circumference above thumb. The smallest size will also fit a teenager.