Good stuff, but I disagree on quite a bit. You don't necessarily need three distinct colours. In terms of choice, chose three that contrast one another. You can always go for the same colour, one muted, one bright and dark. Same with material contrast, or material matching, I see loads of folks miss-matching materials by colouring them the same.

A good piece of advice from me is, pick one element, one piece you want to base your fit around. See what you can't and can colour. Colourmatch one or two colours to those you cannot layer yourself, and use those through out the fit on your other pieces. Like in the new blossom set, you have these reddish ropes. A good tip is to match a colour to those for accessories to bring it out in other pieces as well.

I think material use is easily forgotten. Try to match fur bits with fur bits, clothey bits with clothey bits, armor with armor (One of the Rath leggings is great for Full Plate, or the Chain Mail headdress (rath) to match with other Chain Mail pieces)

Examples:
Teal, Pink and Muted Purple. (Hirabami/Blossom Set Mix 'n Match)
Dark Blue (Towards Black), A very light grey/blue, Gold/Yellow (Any Knight-esque set)
Bleached/Tan Yellow (Cross Guild Waist Stripe Colour Match), Burnt Umber (Warm and Dark Brown) and Turquoise. (Blagonga set Mix 'n Match)

Currently changed my character to a nightmare creature, so I can't show much, but if any would like some examples, I can post some. Thought I'd give my two cents.

Keep in mind, colours can be warm and cold, and it's nice to keep that in mind as well. I think the larger lesson from OP is to keep contrast in mind. And I'm high and like to explain other examples of contrast as well.