I found it really helpful when starting off with MMU to learn about the colour wheel. (This is a great site to learn about colour theory!) We bought one from the scrapbooking store so we could consult it while blending. Colours across the wheel are complementary, so they make the other stand out. I do a lot of combining green with red or pink to get a greener green.
TKB Trading pop micas work on this principle, and you can get some awesome blends from these 7 micas. (And remember, I don't take advertising or sponsorship, so I'm recommending these because I like them!)
I find it hard to explain the colour wheel, so my suggestion is to try it. Combine a red mica with a green mica, a violet mica with a green or yellow mica, or an orange mica with a blue mica and see what you get! You'd be amazed at what comes together when you are mixing colours you'd never ever think of combining! (And yes, you will get some hideous colours you hate!)
What does it mean when a colour is warm or cool? A warm colour is generally one with yellow tones; a cool colour is generally one with blue tones. There are hundreds of definitions of what makes a cool colour cool and a warm colour warm - I like to think of warm colours as being gold and cool colours being silver.
Voyageur carries two types of black - black-blue and black-brown. When I'm creating colours I might like to wear, I always use the black-blue as I'm a cool colour (pale skin with red, brown hair, green eyes). If you are a warm colour, choose the black-brown.
I recommend everyone have brown and black (either shade) iron oxide in their mineral make-up kit, and I recommend gold, silver, and white mica for every kit as well.
WARMING UP A COOL COLOUR, COOLING DOWN A WARM COLOUR
How can you warm up a cool colour - like purple - or cool down a warm colour - like brown?
I started with a 2:1 ratio of base to ultramarine purple. Then I thought I'd add some paradise sand - a brown mica with some pink highlights, which is definitely a warm colour. I mixed 2:1:2 base, ultramarine purple, and paradise sand mica to get the middle colour. Then I added some more paradise sand - just to see what would happen - then finally added 1 more part of ultramarine purple. The last swatch is the one I'd use as a warm purple colour. (Adding brown will get you a plum type purple!)
With the brown I've done a similar thing...I started with a 3:1 mix of base to brown-umber iron oxide. I added 1 part gold mica to the next batch - you can't see the flecks of gold, but it is really nice. For the third batch, I added 1 part arctic silver mica. Again, you can see the sparkles, but it is very nice and glittery! The fourth batch is the third batch with 1 part ultramarine pink in there to cool the colour down again.
A pink is generally a cool colour, but we can warm it up by the inclusion of golds or browns or oranges (although #3 didn't turn out as well as I had hoped - it was just orange). The last swatch is a 3:3:1 ratio of base, ultramarine pink, and red mica, which has a blue tone to it.
Join me tomorrow for the translucent blush base when we'll be warming up or cooling down blush colours!