Fingernail colors are not expressed in RGB. Each color can be expressed in RGB, but RGB is used to define a color in computing, while paint uses other standards.

rgb

RGB is color model and is used to describe colors using numbers and to determine number of possible colors. You can change color model from Image > Mode > choose color model. RGB is suitable for screen and different devices including internet. Other color modes are CMYK suitable for professional printing, Lab, Grayscale.

Although RGB is mainly for devices and screens it is recommended to work in this color mode before converting to CMYK.

Different color spaces within color mode can contain different range and number of possible colors in document (image). RGB color mode have different spaces like sRGB which can contain less colors then Adobe RGB but is supported by most browsers while browsers do not support Adobe RGB color profile, so when you want to post images on internet or send them on email first convert to sRGB profile (space) from File > Save for Web & Devices (turn on Convert to sRGB) or Edit > Convert to Profile > RGB > sRGB IEC61966-2.1.

ProPhoto RGB is largest color space and is designed for feature devices and printers...

Movies use additive color, also known as RGB color. Colored light is projected onto a screen, so the end visual is reflective, but the color is additive RGB.