We're used to seeing the RGB color like a combination of 3 numbers in a range of 0 to 255. Each number represents the intensity of red, green, and blue. This color model is wildly popular on the web as the mix of colors in different intensities produces millions of colors on screens.

But what does the "A" stands for in the RGBA acronym? It refers to the alpha channel, which specifies the opacity for a color. The number 0.0 means the color is fully transparent and 1.0 — completely dense and opaque.