RGBA color values are $....$

Group of answer choices

an extension of RGB color values with an sigma channel $-$ which specifies the saturation for a color.

an extension of RGB color values with an alpha channel $-$ which specifies the opacity for a color.

an extension of RGB color values with a beta color $-$ which specifies the hue for a color.

an extension of RGB color values with an delta channel $-$ which specifies the brightness for a color.