Brown is a combination of red, yellow and blue. A method of creating brown is discussed at http://www.wikihow.com/Mix-Paint-Colors-to-Make-Brown The contrasting color depends on the colors in the brown you want to contrast. The tertiary color wheel may be helpful with your search. Color Wheel Chart
Pink is not on the conventional color wheel.
Pink is a tint of red, it's made when you mix red with white. If you were to make a color wheel of tints (light shades) of every color, pink would be opposite light green.
The colour opposite purple in the colour wheel is yellow.
Red is the opposite of green on the colour wheel.
To find examples, just key in 'colour wheel' in your search engine.
peach
Violet
Taupe.
If you look at a color wheel chart, the opposite of blue is orange.
If you Google the color taupe and view the results you'll notice that there are many colors that go by that name. There is no "official" taupe, so if anyone labels a color they've mixed with that name, it's taupe. Taupe is essentially a light gray (black and white) with just a hint of anything from orange to red to purple in it. I've even seen it with a hint of green.
BEIGE
Since denim is a shade of blue, it would be a complementary shade of orange that is opposite of blue on the color wheel.
Taupe.
The color RED is opposite green on the color wheel. (see color wheel at the related link below)
There is no antonym for color wheel.
the opposite colour of yellow is purple on the colour wheel.
On the additive color wheel, the opposite of Orange would be Blue.
the opposite colour to red on the colour wheel is in fact and truely green.
taupe
On the color wheel the opposite of yellow is purple. purple
Complementary colors are opposite to each other on the color wheel.
Colors opposite from each other on the color wheel are called complementary colors.
violet
orange