Kohaku
The Kohaku is the most popular variety of koi. So much so that there is an expression, "Koi avocation begins and ends with Kohaku." There are various tones of "red" color - red with thick crimson, light red, highly homogeneous red, blurred red, and so on.
The beauty of a Kohaku lies in the purity of it's white body and the depth and intensity of the red patterns. The edges of the red markings should be crisp and clear against an unblemished white background. This crisp edge is referred to as the "kiwa".
Kohaku are quite sensitive to water condition. If the water hardness is too high, small black freckles called "shimi" can form on the skin. Softer water will not only prevent shimi from forming but will also encourage the development of the red (Hi).