but RYB is not a standard saying of three primary colors it should be called as RGB or CMY

Correct, in the context of digital color model and additive color mixing, the primary colors are indeed RGB (Red, Green, Blue). The confusion often arises because of two different sets of primary colors used in different mediums:

1. RGB: This set applies to digital display systems such as computer monitors, televisions, and digital cameras. These systems create colors by combining and mixing light from the three primary colors. RGB is an additive color model where the primary colors are added together to produce a broad spectrum of colors.

2. CMY: CMY stands for Cyan, Magenta, Yellow, which are the primary colors in the subtractive color model, often used in color printing. Here, colors are created by reducing (absorbing) parts of the white light source with pigments. Black is added in the CMYK model (Cyan, Magenta, Yellow, Key/Black) to achieve fine details and deep black tones.

RYB (Red, Yellow, Blue) is not a standard set for primary colors but stems from historical and educational usage. It is closer to how color mixing was traditionally taught and simplifies the process of creating secondary colors on paper with pigments. However, RYB doesn't accurately represent the subtractive color mixing in modern color printing as CMY would. Using RYB for color mixing often leads to muddy or duller-seeming results compared to CMY because it does not cover the full color spectrum needed for accurate color reproduction.