What are RGB HEX HSL ?
They are different ways in which you can define a color.
RBG color lets you define the Red/Green/Blue combination from 0 to 255 decimal values. It is usually combined with Alpha (RGBA) to offer an opacity to the color, which you can't achieve in Hex.
HEX color is the most used way of defining a color, by letting you choose how much Red/Green/Blue you want to have in hexadecimal values between 00 and FF.
HSL is mostly used by graphic designers and it lets you define the hue, the saturation and lightness.