Watercolor
Watercolor is a very versatile medium. Personally, it is my favorite medium to use because it is very easy to blend pigments, because is is water based. Watercolor is basically finely grounded pigments that are dissolved in water. The water acts as a carrier of the pigment onto the paper where it seeps in and makes the pigment permanate. Since a good amount of water is absorbed by the paper when painting with watercolors, one should invest in thick paper to paint on so that it will not warp or bend. Another alternative is to tape the corners of the paper so that it will not shrink as the water dries.
Tips on controlling color
As a rule of thumb, the more water that is added the more dilutesd the pigments become, hence the lighter shade it will be, and vice versa. Watercolor is best blended when it is still wet, however too much water can cause the colors to bleed too much into each other and create a mess and too little can result in two seperate colors instead of a continous smooth color. It is handy to have a couple of tissue paper or napkins nearby to soak up the excess water.
In my experience, it is always better to add a little at a time than to add too much at one time. If you add too much water, then you would have to wait till the water evaporates before you can use it to paint. A brush is a good way to keep measure of how much water is added by counting the droplets of water.
Sometimes, a brush can soak up too much water and as a result, it can accidentally drip onto the paper or cause one color to bleed into another. A good tip is to dab the brush onto a napkin before starting to paint.
Also, make sure that you have the desired shade of color before you start painting, since watercolor is unforgiving when it comes to mistakes. It is a good idea to experiment on stratch paper first.