Color-tunable LED light fixtures generally change colors by controlling LEDs of multiple colors. This type of light source requires additional secondary optics and light-mixing distances to deliver color-mixing functions and perform high color uniformity. However, the color-mixing elements increase the optics size, resulting in more difficulties in making tiny lighting fixtures. Therefore, in this study, we introduce a LED primary optics design method that retains standard LED package size while featuring a color-mixing chamber. This method combines a lens having a rotational symmetry with a freeform profile and a zigzag structure by using double total internal reflection to disperse light uniformly. In contrast to a typical hemispherical lens, our design effectively lowers the weighted average color difference from 0.03 to 0.0035, and maintains optical efficiency of at least 90% without using any optical diffuser.