Sublimation printing is only suitable for garments that include polyester (Dri-fit, 100% polyester, or polyester blend). Polyester is a fabric that expands due to heat and takes in the colour through the method of sublimation.
Sublimation inks are essentially a dye, it would be physically impossible to dye a dark garment a lighter colour, hence no white in sublimation inks.
Sublimation works best by printing a design into white or light colored fabrics, Thus, white is considered the color for sublimation, but you can print on light-colored garments, provided you don't need the color white within the image or design.