Here is a link to an online Virtual paint mixing guide from Golden Acrylic paint website.
An indispensable guide if you are having trouble finding a certain color and need the mixing proportions- it also takes the color from a photo (on your computer) and gives you the exact colors to mix to achieve the color.
Now how cool is that?
BUT A word of caution – The trained artists eye and mixing color charts is still an important aspect of artistic skill building. I highly recommend not using graphs, tracing paper, measuring implements, projectors or computer programs to do your art for you. Build your skills and train your eye to see as an artist because it gives life, movement and energy to a piece. Measuring, detail and tightness will often lose a quality in your art that only the artistic eye can achieve. Sacrifice perfection and give yourself permission to explore.-PA