RGBColor

RGBColor[r,g,b] represents a color in the RGB color space, using red, blue and green components. 

RGBColor[r,g,b,a] specifies opacity a. 

RGBColor["string"] returns a color from a hex color or an HTML color name.

RGBColor[color] returns the RGB representation of color.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.